The Binding of Isaac: Rebirth – TBoI Boss Ideas

 

[Prior Notes]

There are a total of 18 bosses on this page, 17 spanning the game’s general progression, as well as one that has its own unique floor and spawning mechanics at the end. Some of them are based off of existing bosses, while others are entirely unique.

There are also 4 bosses with the unique gimmick that they are based on the special DLC variants of the first 4 chapters, grouped together at the end

I will say, however, that I am not amazing at art, and haven’t been able to actually sprite the bosses, so the images are more placeholders to show a general design for the boss

Also, while I know Isaac mods exist, I haven’t had time to really explore them myself, so if there are any bosses similar to modded ones that already exist it wasn’t intentional, sorry

Boss 1 – The Giant

Appearance: A large humanoid with an appearance much like Isaac’s. His lower body is entirely obscured by darkness

Health: 400
Found: Basement, Cellar, Burning Basement
Room: 1×1

Pattern:
The Giant always remains at the upper half of the room, partially-obscured by being stuck in a hole in the ground, attacking infrequently
-It may reach out and slam its fist down, trying to crush the player. The attack is slow and only performed when the player is close to it.

(Damage)
-It may vomit up a cluster of projectiles, similar to Monstro

(Damage, Large Shots)

(Damage, Small Shots)
-It may vomit, launching an arc of 3 shots towards the player

(Damage)

Champion Variants:
-Red Champion: Attacks are significantly faster, but max health is reduced by 10% (360)
-Grey Champion: The fist slam attack creates a ring of rocks around the fist. Doesn’t perform the 3-shot arc attack

Extra Info:
-The Giant was the first boss designed for this page, and was also one of the 2 earliest concepts alongside the Kraken
-The Giant has the most health of any Basement boss, beating out even Dingle’s 300 health.
-The Giant’s arena was originally intended to be 1×2, to accommodate for its size, but this was later scrapped due to similarities with an existing boss
[Added: 21/12/20]

Boss 2 – Goliath

Appearance: A posthumous version of the Giant. Its body is mostly red and fleshy, and he has a hole in his chest. It seems to be wearing a skull, similar to a Host, covering most of its head.

Health: 600
Found: Caves, Catacombs, Flooded Caves
Room: 1×1

Pattern:
Goliath, like the Giant, is trapped in a hole at the top of the room. However, there are also 2 doors to the sides of the room that the player cannot enter from or interact with.
Phase 1:
The Giant attacks in a cycle; using 3 attacks before lifting up its skull hat. He is invulnerable while the skull hat is down
-He may move to one side of the pit, based on what side the player is closest to, and reach his arm through the door: feeling around before bringing his arm back through the door

(Damage)
-He may vomit up a lengthy barrage of blood shots, similar to Monstro’s, though the barrage lasts for over a second

(Damage, Small Shots)

(Damage, Large Shots)
-He may vomit up a vertical column of red damaging creep across the floor

(Damage)
-He may release 3 arcs of shots at the player, each consisting of 3 shots each

(Damage)
-He may slam one of his arms down, creating a pool of red creep around where the fist lands

(Damage)

(Damage, Creep)
Once Goliath uses 3 attacks, it will roar and look upward. If attacked in this state, his hat will be knocked off, beginning Phase 2
Phase 2:
With the skull removed, Goliath will become vulnerable and will remain as such for the rest of the fight
Goliath retains all previous attacks, but no longer takes breaks to roar at the player.

Champion Variants:
-Green Champion – Replaces the ‘arc shot’ attack with an attack where it launches 3 ipecac shots inaccurately
-Red Champion – Increases its max health by 20% (720), though it is vulnerable throughout the entire fight. The hat does not need to be knocked off. Additionally, the ‘door’ attack leaves red creep behind.

Extra Info:
-Goliath is tied with Mega Fatty for having the most health of any Caves boss, with 600, and beating Gurdy by 5 health.
-Keeping away from the doors can make the ‘door’ attack ineffective, and similarly keeping away from the edge can negate the ‘fist slam’ attack
–Flight also renders both the creep-using attacks less dangerous
–Staying at the back of the room, near the entry door, is generally a good idea due to giving the player more time to react, and putting them out of reach of 2 of the boss’ attacks
[Added: 21/12/20]

Boss 3 – Centipede

Appearance: A large insect-like monster with a single, beady eye at its front. It seems to have blood running down its belly, and several spindly legs starting from around the middle segment of its body

Health: 275
Found: Basement, Cellar
Room: 1×1

Pattern:
The room the Centipede spawns in has various cracks in the walls.
The Centipede will spend most of its time bursting from random parts of the walls before burrowing back into the opposite wall, travelling in a straight line

(Damage)
Additionally, it may sometimes crawl along its belly between two holes, creating a short-life trail of damaging red creep.

(Damage, Creep)
As her health lowers, the Centipede’s speed gradually increases.

Champion Variants:
-White Champion: Replaces the red creep attack with an attack that releases a pool of slowing white creep and 1-2 Sacks when moving across the room.
-Black Champion: Leaves slowing black creep whenever it moves. Does not spawn red creep.

Extra Info:
-Due to being a worm-like boss, Centipede is very vulnerable to piercing shots, such as Technology, Brimstone, or Cupid’s Arrow
–Damaging creep abilities are also effective for similar reasons
[Added: 21/12/20]

Boss 4 – The Brittle

Appearance: A posthumous version of the Centipede. Its eye is now replaced with a mouth of sharp teeth, its legs are more fin-like in movement and are shorter and stubbier, and most of its body is covered in thick plating

Health: 270
Found: Depths, Necropolis, Dank Depths
Room: 1×1

Pattern:
Brittle acts similar to her live counterpart, bursting out of cracked walls to attack the player. Her actions are less predictable than Centipede’s, however.
Brittle’s body is mostly invulnerable to attacks due to the plating. However, when it bursts out of the wall, one of its segments will randomly have a broken piece of plating the player can damage Brittle by attacking
-It may charge out of the wall and rush to the wall parallel in a straight line, similar to how Centipede would. It leaves a red creep trail as it does so

(Damage)

(Damage, Creep)
-It may pop out partially from a wall and launch several clusters of blood shots towards the player. All the shots, while launched at random speeds, are all launched in the same straight line in the player’s direction from where Brittle emerged

(Damage)
-It may burst out of the wall, landing near the centre of the room. It will flail about for a few seconds before flinging itself back into a nearby wall. Its flailing leaves creep, alongside the contact damage risk

(Damage)
-It may pop out partially from a wall and launch a barrage of shots. It starts from a random angle, swinging gradually towards the player, and stops firing about 1.5 seconds later, returning to the wall

(Damage)

Champion Variants:
-Red Champion – Has 50% more health (450), but all segments are vulnerable to damage
-Black Champion – Shot barrage attacks replaced with brimstone lasers. Lasers deal a full heart of damage instead of half a heart

Extra Info:
-Brittle’s regular form has the least health of any Depths-specific boss, with less than half of what Monstro II has and nearly only a third of the Cage’s health
–This is because, unlike those bosses, Brittle spends much of its time immune to damage
-Piercing shots are very helpful for this fight, as they can pass through the invulnerable segments to hit the vulnerable one
[Added: 21/12/20]

Boss 5 – Rot

Appearance: A posthumous version of the Husk, who was already a posthumous version of the Duke of Flies.

Health: 475
Found: Depths, Necropolis, Dank Depths
Room: 1×1

Pattern:
Flies around the room diagonally, spawning Spits and Guts or dealing contact damage

(Damage)
While it does not take damage from the ipecac shots from the Guts and Spits, being hit by them will cause Rot to begin flying more rapidly for a second, spawn 3-4 Spits rapidly over this time, and leave a trail of damaging green creep as it moves.

(Damage)
It can also ‘eat’ its own Spits if one is in its movement path. If it does so Rot will bite the Spit, killing it, and then spit out 2 ipecac shots towards the player

(Damage)
As it loses health, Rot slowly gains speed and begins spawning enemies more frequently

Champion Variants:
-Red Champion – Spawns Boils and Suckers instead of Spits and Guts, cannot leave creep due to its summons lacking explosive shots, and upon eating a Sucker launches 8 shots in the cardinal and ordinal directions. Also has 10% more health (523)
-Black Champion – Spawns Dank Squirts and Clots instead of Spits and Guts, always leaves a trail of black slowing creep as it moves, and cannot eat any of its minions. Has 20% increased health (570)

Extra Info:
-Explosion immunity and flight are both very helpful for this fight defensively, as they make some of its attacks significantly weaker, and piercing helps for dealing with its minions faster
-Rot is a posthumous boss of a posthumous boss, something that otherwise does not exist in regular Isaac
[Added: 21/12/20]

Boss 6 – Bomber Boy

Appearance: A small Isaac-like monster carrying bombs. He has an eyepatch over his right eye and several burn marks over their body, presumably from bomb explosions

Health: 200
Found: Basement, Burning Basement
Room: 1×1

Pattern:
Bomber Boy always has a large pile of explosives sat at the top-centre of the room that blocks player movement, but serves little other function to the player.
Bomber Boy will usually jump onto the pile of bombs, pick up 2 bombs, and then jump down and attack.
When off the pile, Bomber Boy will chase the player, throwing bombs at the player infrequently, as long as he has bombs remaining. The bombs are launched similar to Dr. Fetus, and Bomber Boy can take damage if maneuvered back into one of his own bombs.

(Damage)

(Damage, Bomb)
After exhausting the bombs he picks up, he runs away from the player for a couple of seconds before jumping back onto the bomb pile and repeating the cycle.
Once his health is exhausted, he will jump back onto the pile, but will get stuck. The pile of bombs will explode after a couple of seconds, and can damage the player if they are too close

Champion Variants:
-Red Champion – Only picks up 1 bomb at a time from the bomb pile, but the bombs have have the bobby bomb and hot bomb effects, chasing the player and leaving lingering fire upon exploding
-Black Champion – Moves slower, but has 10% more health (220) and is now immune to his own bomb explosions

Extra Info:
-Bomber Boy is one of few bosses that can potentially score a posthumous kill against the player, due to the bomb pile he lands on exploding after he is defeated
-With Host Hat or Pyromaniac, most variants of this boss can be made pathetically easy, as they negate the bomb explosions which are otherwise Bomber Boy’s main form of damage
–Safety Scissors can also make this fight laughably easy
-Bomber Boy’s actions and movements are very similar to those of Wrath; attacking the player with a barrage of lit bombs
[Added: 21/12/20]

Boss 7 – Pyro

Appearance: A posthumous Bomber Boy, left primarily as a skeleton. It carries a single sack of bombs on its back, seemingly one from the pile of bombs that Bomber Boy had previously

Health: 320
Found: Caves, Catacombs, Flooded Caves
Room: 1×1

Pattern:
Pyro will chase the player, sometimes stopping to throw one of various bombs towards the player. Unlike his live counterpart, he doesn’t need to consult any props in the arena. His various bomb attacks are based on types the player can use.

(Damage)
-May throw a homing bomb that chases the player and explodes into a ‘+’ shape of explosions upon detonating

(Damage)
-May throw an orange-tinted burning bomb that explodes with a large explosion radius and leaves a lingering fire where it exploded

(Damage)

(Damage, Contact)

(Damage, Fire)
-May throw a green-tinted bomb towards the player that leaves a trail of creep as it travels, and explodes into a larger pool of creep upon exploding

(Damage)

(Damage, Creep)
Upon death, Pyro will explode after a short while

Champion Variants:
-Orange Champion – Bombs thrown do not have additional effects, though they are thrown with greater force and are thrown more rapidly than normal
-Black Champion – Health increased by 10% (352) but moves slower. Immune to its own bomb explosions

Extra Info:
-As with Bomber Boy, Host Hat or Pyromaniac make the fight significantly easier
–Flight also makes a noticeable difference, as it makes the creep bombs far less dangerous and allows the player to completely outmaneuver Pyro
–Safety Scissors make the boss laughably easy, as the only attacks it can hurt the player with are the creep bomb’s creep trail when thrown, and contact with the orange fiery bomb, and Pyro’s contact damage
[Added: 21/12/20]

Boss 8 – Larry Sr.

Appearance: A skeletal version of Larry Jr.; seemingly picked clean by the catacomb’s denizens.
[Unlock: Kill Larry Jr. and the Hollow (Boss Variants)]

Health: 32 (Per Segment)
Found: Catacombs
Room: 1×1

Pattern:
Larry Sr. moves around, like Larry Jr. does. It does not spawn poops like Larry, and is capable of destroying both poops and rocks by headbutting them.

(Damage)
It may sometimes stop moving, only to vomit a cluster of bones out in front of itself

(Damage)
It may stop moving and launch 3 bones towards the player in rapid succession

(Damage)
Damaging its segments may cause it to spawn Attack Flies and Moters
Destroying its segments can spawn enemies from the destroyed segments:
-Charger
-Spitty
-Sucker
-Bony

Champion Variants:
-Blue Champion – Does not spawn enemies when a segment is destroyed, instead launching 4 bones in the cardinal directions
-Black Champion – Segments explode when destroyed, spawning a Black Bony in its place after the explosion

Extra Info:
-This is the 2nd posthumous Larry Jr. boss, with the first being the Hollow
-Larry Sr.’s concept was based on the fact that, despite encountering a Larry Jr., no Larry Sr. is seen in the game
-Piercing shots are, as ever, highly effective against Larry Sr.
[Added: 21/12/20]

Boss 9 – Buzzkill

Appearance: A large, bloated fly. It has what seems like a large eyeball where a mouth may have been. Its wings seem too small to carry it.

Health: 350
Found: Basement, Cellar, Burning Basement
Room: 1×1

Pattern:
Buzzkill will fly around the room diagonally, much like a Boom Fly, when not attacking. It will frequently stop to attack the player directly.

(Damage)
-It may turn to face the player and launch a large blood shot from its eye at the player that leaves a trail of creep as it travels

(Damage)

(Damage, Creep)
-It may perform its first attack, but will launch a total of 3 of these blood shots in succession

(Damage)

(Damage, Creep)
-It may charge at the player directly, moving in one direction until it crashes into a wall. After hitting a wall it falls down, leaving creep where it lands, before getting back up and flying around again

(Damage)

(Damage, Creep)
Once down to 50 health, it will perform its first attack again, but instead launches its eye at the player instead of a blood shot. After this point, Buzzkill can only fly around and use its charge attack until it dies, losing access to its 2 projectile attacks.

Champion Variants:
-Black Champion – Gains 10% health (385), but no longer shoots its eye when below 50 health, thus never losing access to any of its attacks. Upon death it will only then shoot its eye, just before dying.
-Green Champion – Launches Ipecac shots instead of the blood shots. When the Ipecac shots land they leave large creep trails. Immune to its own explosions.

Extra Info:
-If killed before it launches its eye (Regular variant and Green Champion) the death animation will still show its eye absent
-Buzzkill was originally dubbed ‘Polyflymus’, due to the large Polyphemus-like eye in its mouth
-Buzzkill’s appearance and basic movements are highly similar to those of Boom Flies. Its Ipecac-launching champion variant only further cements this similarity
[Added: 21/12/20]

Boss 10 – Horrid Horseman

Appearance: A posthumous version of the Headless Horseman, with a rotten green body and additional decay.
[Unlock: Kill the Headless Horseman (Boss)]

Health: 200 (Head), 250 (Body)
Found:
-Caves, Catacombs, Flooded Caves (If Headless Horseman was defeated in the Basement layer)
-Depths, Necropolis, Dank Depths, Womb, Utero, Scarred Womb
Room: 1×1

Pattern:
The Head and Body attack separately, and have their own attacks
The Head will float around the room randomly, sometimes attacking the player with either projectiles or contact damage

(Damage)
-It may fire 3 shots in an arc at the player

(Damage)
-It may flop onto the ground, launching 4 shots in the cardinal directions and spawning green creep beneath itself

(Damage)

(Damage, Creep)
-It may flop onto the ground and begin spinning around, chasing the player, and spawning green creep as it does so. A couple of seconds later it will stop and begin floating again

(Damage)
The Body, like the head, floats randomly around the room, dealing either contact damage or attacking with projectiles

(Damage)
-If horizontally aligned with the player it may charge at them over a very short distance, spawning green creep beneath it

(Damage)
-It may launch 2 rapid-fire ipecac shots at the player that leave lingering creep upon exploding

(Damage)

(Damage, Creep)
Both the Head and Body must be killed to end the fight

Champion Variants:
[None]

Extra Info:
-While the Horrid Horseman is normally a boss found in Chapters 3 and 4, it can be forced to spawn in Chapter 2 if the player kills a Headless Horseman in Chapter 1. It isn’t a guarantee it will spawn even if the player does meet these criteria, however
-As with the other ‘special’ horsemen, the Horrid Horseman has its own unique drop instead of dropping an item from the boss pool upon defeat
[Added: 22/12/20]

Boss 11 – Spiderball!

Appearance: A colossal mass of Spiders, grouped together to form an even larger and more powerful spider
[Unlock: Undergo the Spider Baby transformation]

Health: 50*
Found: Caves, Catacombs
Room: 1×1

Pattern:
Spiderball! moves sporadically around the room, sometimes skittering at the player like Spiders and Big Spiders do.
It cannot be directly harmed, and must be harmed by killing its minions instead. It can either be forced to spawn minions by attacking Spiderball! (though this doesn’t directly harm the boss) or will spawn minions when attacking

(Damage)
-It may charge at the player, only stopping when it hits a wall, causing it to spawn 2 random minions

(Damage)
-It may jump up into the air and out of sight, before landing down upon the player

(Damage)
The various minions it can spawn are all worth various amounts of ‘damage’ towards its health bar:
-Spider: 1
-Big Spider, Lv. 2 Spider, Trite: 2
-Ticking Spider, Small Baby Long Legs, Small Crazy Long Legs: 3
-Baby Long Legs, Crazy Long Legs: 4

Champion Variants:
[None]

Extra Info:
-The Big Spider’s spawned Spiders count towards Spiderball’s health, as do any spawned from the Baby Long Legs’ spawned Sacks
–The Sacks themselves do not count, however
-Familiars will not intentionally target Spiderball, but can still hit it when attacking
-Spiderball gets smaller as it loses health
-Spiderball is a visual pun based on the term ‘black mass’, meaning a gathering of witches
[Added: 21/12/20]

Boss 12 – The Kraken

Appearance: The boss actually consists of 4 entities; 3 Sirens, and the Kraken itself
The Sirens have red coverings and blonde hair with a single horn protruding from it at the side. Their bodies are almost entirely black
The Kraken itself is a large and grotesque monster with a gaping mouth and several tentacles. Its lumpy body is obscured throughout part of the fight, and even when it shows some of itself its bottom half is still obscured by water
[Unlock: Complete Chapter 5 and have unlocked the Flooded Caves]

Health: 100 (Sirens), 475 (Kraken)
Found: Depths, Dank Depths
Room: 1×2

Pattern:
The Boss Room itself doesn’t actually contain the Kraken, instead forcing the player to drop down a large hole in the centre of the room. Doing so drops the player onto a platform surrounded by water, with the 3 Sirens sat to the sides and behind the platform and a vast pool of water in front
The Sirens are the only target at this point
Phase 1:
The Sirens do not directly attack the player, instead spawning music notes that direct the attacks of the obscured Kraken.
-They may sing notes that begin orbiting the player. A tentacle will emerge from the water and slam down, trying to crush the player

(Damage)
-They may sing several notes that travel to random parts of the arena. After a short time several shots will erupt from the water, landing where the notes rested and leaving slippery blue creep

(Damage)
-They may sing several notes that align horizontally, though spaced-out randomly. Tentacles will emerge and slam down vertically down where the notes were

(Damage)
As each Siren is defeated, they dive back into the water. With each defeated Siren, less notes are spawned but the singing generally becomes faster, increasing attack frequency.
Once all 3 Sirens are defeated, the Kraken itself will emerge from the water
Phase 2:
The Kraken is now vulnerable and is the central focus. It stays at the top of the arena the entire fight.
-The Kraken retains versions of all the Phase 1 attacks, though does not have the Siren’s notes to dictate which attack is being used and where they are aimed
-The Kraken may cause a short wave to wash over the arena, pushing Isaac away and covering the whole platform in slippery blue creep for a while
-The Kraken may launch 5 arcs of shots in rapid succession. Each has 7 projectiles, and each subsequent arc has a slightly different angle, adjusted either clockwise or anti-clockwise

(Damage)
-The Kraken may launch a blue brimstone-like laser across the middle of the arena from its mouth. Slippery blue creep is left after the attack

(Damage)
Upon defeat, the Kraken will sink into the water, and several platforms will arise from the water that lead to a door at the top of the room. Going through leads to a room with the trap door to the next floor, and an item from the boss pool (as well as a Deal or an Angel Room, if applicable).

Champion Variants:
[None]

Extra Info:
-The Kraken is one of very few bosses to have a unique pre-fight room, being a mostly-empty room with a hole in the middle in-place of the regular boss room, and a unique room to fight it in.
-The Kraken is the only boss aside from ???’s boss to utilise slippery blue creep as an attack
-This boss shares similarities to the [Golden Door Boss], due to having a ‘warm-up’ room before the fight, a 1×2 arena, 2 phases, and a giant brimstone-like laser attack
-There was a custom character unlock associated with this boss, which may be elaborated upon later…
[Added: 22/12/20]

Boss 13 – Scorched Serpent

Appearance: A fiery version of Larry Jr. Its body is on fire, aside from its head. Its head seems to lack eyes like Larry Jr. normally has, and has pointier teeth
[Unlock: Unlock the Burning Basement]

Health: 30 (Per Segment)
Found: Burning Basement
Room: 1×1

Pattern:
The Scorched Serpents move similar to Larry Jr., moving unpredictably while mainly trying to melee the player

(Damage)
-They may speed up temporarily, leaving a trail of fire that lingers behind them for a short time

(Damage)

(Damage, Fire)
-They may stop and launch a single flame forward, similar to the Red Candle

(Damage)

(Damage, Fire)
When a segment is destroyed, it may trigger the speed-up/fire trail attack prematurely. This becomes more common the smaller a Serpent gets

Champion Variants:
-Orange Champion – Segments leave a lingering fire when destroyed. Does not trigger the speed-up/fire trail attack when segments are destroyed.

Extra Info:
-This is one of the 4 ‘themed’ bosses: a group of well-known bosses themed around the extra floor themes. This boss is a Larry Jr.-like boss themed around, and fought in, the Burning Basement
[Added: 21/12/20]

Boss 14 – Glob

Appearance: A flood-themed version of Monstro, fitting the theming of the Flooded Caves
[Unlock: Unlock the Flooded Caves]

Health: 400
Found: Flooded Caves
Room: 1×1

Pattern:
Acts similar to Monstro, hopping towards the player when not attacking in an attempt to land on them

(Damage)
-It may vomit several blue tears into the air. They disappear off-screen briefly before raining down again, like the Tube Worm enemies.

(Damage)
-Glob may squash itself down, creating a huge pool of slowing blue creep around itself
-Glob may jump up into the air, eventually landing down again above the player. It launches 8 shots out in the cardinal and ordinal directions upon landing.

(Damage)

Champion Variants:
-Green Champion – Vomit projectiles have ipecac properties, and the creep pool is replaced with a smaller pool of damaging green creep instead
-Black Champion – Vomit attack no longer spawns projectiles, instead spawning 1-2 Drowned Chargers. 10% more health (440).

Extra Info:
-Glob is the 2nd of the 4 bosses themed around the DLC floor themed, being a Monstro themed around the Flooded Caves
-Despite being directly linked to Monstro, it also has behaviour akin to Monstro II, with its leap attack and its effects, and its Green Champion’s ability to spawn minions.
–It also shares extra similarities to Gish, primarily the slowing creep, and the Green Champion’s ipecac shots
[Added: 21/12/20]

Boss 15 – Gush

Appearance: A Dank Depths-themed variant of Chub. Its body appears to be made of oily sludge, and it has hollow black eyes with yellow dots within them
[Unlock: Unlock the Dank Depths]

Health: 600
Found: Dank Depths
Room: 1×1

Pattern:
Moves around the room, like Chub, spawning a trail of black creep as it moves. When aligned with the player in its field of view it will roar and charge at them, destroying obstacles and enemies and ending only when it slams into a wall.

(Damage)
It may open its mouth, launching various globules of black ipecac into the air that land in random locations near Gush. These leave black creep where they land.

(Damage)
It may spawn enemies from its back. These enemies will either be 2 Dank Chargers, 2 Clots, a Tar Boy, or a Dank Squirt
At 33% health it will split into 2 smaller Gushes. These 100-health mini-Gushes have similar attacks to the larger version, though spawn less black ipecac shots and their summon attacks can only summon 1 Dank Charger or 1 Clot when used.

Champion Variants:
-Red Champion – Ipecac shots now leave red ipecac when they land. Spawns Boils instead of Tar Boys
-Yellow Champion – Has 20% less health (480), though spawns a half-health Chub upon death

Extra Info:
-Gush, as its appearance suggests, is a hybrid between Gish and Chub. It is the third of the DLC floor-themed bosses, based on the Dank Depths.
-It is actually a deceptively rare boss, since it can only be encountered in Dank Depths 1; a single floor, requires a specific theme for said floor, and the theme itself needs to have been unlocked already
–If all 3 Chapter 3 themes have the same spawn chance, as do all bosses, the floor is a 1 in 3 chance and a 1 in 12 when counting existing bosses, meaning roughly a 1 in 36 chance to encounter Gush during a run (not factoring in other bosses from this page, or items that can affect boss spawns like Book of Revelations), or around a 2.78% chance
-Flight makes this boss significantly easier, as it negates the slowing creep that would otherwise litter the arena floor
[Added: 21/12/20]

Boss 16 – The Conjoined

Appearance: The floor-themed version of the Gemini boss. Instead of a single smaller person attached to Conjoined, three heads protrude from a scar in the back of its head. Conjoined’s own eyes are also noticeably swollen over
[Unlock: Unlock the Scarred Womb stage]

Health: 700
Found: Scarred Womb
Room: 2×1

Pattern:
Conjoined’s room always has an effect similar to Curse of Darkness, obscuring the player’s view while the boss is alive.
Conjoined will wander the room until it ‘detects’ the player. If the player was detected by Conjoined itself it will charge at them, only stopping when it slams into a wall, and if its smaller heads see the player they will shriek, and the Conjoined will chase the player similar to how Gemini normally does for a few seconds before performing the charge attack. The chasing and charge also spawn creep, and the Conjoined can break rocks, poop, and is immune to spikes when charging.

(Damage)

(Damage, Creep)
After a charge has occurred, the three heads will do one of three attacks:
-They may launch a total of 4 arcs of shots at the player, with each arc having 3 shots. The angles of the arcs are actually not directly at the player, and are at slightly offset angles

(Damage)
-They may all launch streams of red shots at the player over 2-3 seconds

(Damage)
-They may shoot 3 brimstone lasers: 1 directly behind the Conjoined, and the other 2 at 45-degree angles of the first laser

(Damage)
After the smaller heads attack, the cycle repeats again
However, once below half health, the Conjoined will begin following the player as opposed to walking around randomly, making him seem more aggressive and making charges more frequent

Champion Variants:
[None]

Extra Info:
-This is the 4th and final floor-themed boss, being a Gemini boss themed on the Scarred Womb.
–Though, despite being themed around the Gemini boss, it lacks the gimmick of the smaller Gemini breaking off to attack the player that is otherwise present in both the Gemini and Steven fights
-Much like Gush, this boss is statistically rarer than other bosses, as it is only capable of appearing on Scarred Womb I
–If the floor theme is considered a 1 in 3 chance again, and a 1 in 15 chance for bosses (also excluding other Womb-themed bosses from this page), then there is only a 1 in 45 chance of encountering the Conjoined in a run, even less than Gush (Excluding other bosses from this page, and also excluding items like Book of Revelations that can affect boss spawns). These chances are roughly only a 2.22% chance per run
-The smaller heads of Conjoined may be a reference to the transformation of the same name that grants the player 2 smaller heads and a triple-shot
[Added: 22/12/20]

Boss 17 – Rotten Heart

Appearance: A rotten heart with a physical appearance based on Mom’s Heart. Its colours are now greens and browns, and seems to be leaking a greyish-brown liquid (though on the splash screen it appears more of a deep brown)
[Unlock: Defeat It Lives! as 5 different characters. A door then has a chance to appear after defeating It Lives! in the boss room with around a 30% chance, though the chance can be increased by another 25% by beating Boss Rush and 25% more by beating It Lives! in under 30 minutes, or using the Bible on It Lives! will increase it to 100%]

Health: 2,000
Found: Womb, Utero, Scarred Womb
Room: 1×1

Pattern:
Before the player fights the Rotten Heart, they will find themselves in a room with 2 item pedestals containing 2 boss items. Taking one of these will cause the other to vanish, the entrance to be barred shut, and another door to appear in the room. Entering this door takes the player to the Rotten Heart fight.

The Rotten Heart itself will be at the centre of the room, pulsing slowly but rhythmically. Its attack patterns are reminiscent of It Lives!’, with it attacking the player directly before summoning minions, though it only summons its minions at set health percentages instead of after every attack. It unlocks new attacks every time one of its minions is killed
Phase 1:
-It may fire 4 grey brimstone lasers in the cardinal directions and rotate them 180 degrees

(Damage)
–It may perform another version where they are rotated 360 degrees instead

(Damage)
-It may shoot a stream of grey tears at the player in rapid succession over 3-4 seconds

(Damage)
Once down to 1,600 health it retreats to the ceiling and summons one of 4 bosses. It does not attack while these bosses are active.
-Dark One
-Peep
-Chub
-The Stain
Once the boss is defeated it drops down from the ceiling again and begins attacking once more
Phase 2:
Retains all previous attacks, as well as gaining some new ones
-It may shoot large greyish tears at the player that leave trails of creep where they explode, usually exploding where the player was standing when the attack was launched. Does this up to 3 times in succession

(Damage)

(Damage, Creep)
-It may beat harder for a single beat, causing a wave of rocks to travel from one wall to the adjacent wall. This creates several lingering rocks. Afterwards it will fire a grey brimstone laser that sweeps across the whole room twice rapidly, but it does not pass the rocks, allowing the player to use them as cover to avoid damage. Afterwards, the rocks break again

(Damage, Rock Wave)

(Damage, Brimstone)
At 1,200 health it retreats to the ceiling, summoning another boss. This time it will fire a stream of grey tears starting from the top left and gradually sweeping over to the top right of the room, and then back again.
The pool of bosses is the same as before, but it will not choose the same boss as previously chosen, whichever it was. Once the boss is defeated, the heart drops down again.
Phase 3:
Retains all previous attacks, and gains two new ones
-It may summon a large grey tear that bounces around the room for a few seconds before exploding. It leaves damaging grey creep wherever it moves and creates a larger pool upon exploding

(Damage)

(Damage, Creep)
-It may summon a large grey tear that chases the player for a few seconds before shrinking and vanishing. It leaves damaging grey creep as it travels

(Damage)

(Damage, Creep)
At 800 health it retreats to the ceiling, summoning another boss. While the boss is active the Rotten Heart acts similar to Mom’s Heart; launching wide arcs of 4 grey tears roughly every second with each subsequent shot being at a slightly different angle. The boss pool, unlike before, is different:
-Adversary
-Teratoma
-Sister Vis
-Monstro II
Once the boss is defeated the Rotten Heart will drop down again
Phase 4:
Gains access to all of Mom’s Heart’s attacks alongside its own. Noticeably speeds up many of its attacks as well
Upon reducing the boss to 400 health it retreats back to the ceiling and summons the 4th and final boss. It will summon one of the 4 from the latter boss pool, but not the same boss as summoned previously
Once the boss is defeated the Rotten Heart will drop down for the final time
Phase 5:
The Rotten Heart’s beating begins to slow. Each ‘beat’ causes it to release a burst of grey tears evenly-spaced at an angle. As it loses health it slows down, but spawns more tears per beat. It does this until it is defeated

(Damage)
Killing the boss will provide the player with 1 of 2 rewards: both from the boss pool. It also allows the player to leave the room and unlocks the previously-sealed door from the original item room, allowing the player to re-enter the It Lives! boss room and progress further

Champion Variants:
[None]

Extra Info:
-Unlike Mom’s Heart and It Lives!, the Rotten Heart’s heartbeat will actually slow down as it loses health instead of speeding up
-Originally this was planned to be a more secretive boss, only found after killing It Lives! and using one of various razor-like items to open the room, though this was later scrapped
-Killing the Rotten Heart can open the Void Portal, even though it doesn’t grant access to any other levels without the player exiting the room
-Like with Boss Rush, Mama Mega and Dad’s Key can force the Rotten Heart’s room to open
-If an item like Equilibrium is used, and the player beats It Lives! in under 30 minutes, the Rotten Heart’s room will be overridden by the other 3 rooms. Waiting until 30 minutes pass, or by using the Deal/Angel Rooms, the player can make the Rotten Heart’s room appear properly
[Added: 22/12/20]

Boss 18 – Sandman

Appearance: A shadowy skull, mostly obscured by the darkness. It has 3 red dots that move around in its left socket as some sort of eye or eyes.

[Unlock:]
-The player must have already unlocked It Lives! previously
-The player must defeat [???]’s boss and [Golden Door]’s boss previously
-The player must have the Polaroid and Negative
-The player must have completed the Boss Rush for at least 1 character
Afterwards, the player has to fulfil certain criteria per run:
-The player must have taken either the Polaroid or Negative
-The player must defeat [???]’s boss on the current run
Upon fulfilling the criteria, the room that spawns at the back of the arena that normally spawns the portal to the Void will be altered, making a new room appear in its place 100% of the time, and making the Void portal itself spawns roughly 50% of the time beside it
Taking the new path will take the player to a floor called the Polaroid

The Polaroid floor is a mostly grayscale floor designed to look similar to the Bedroom special rooms. There are 4 gold chests in the starting room, and a shop south of the starting room. The player must travel north, with the first 8 rooms north containing 8 bosses, those being the 8 that the player encountered in the boss rooms throughout the game starting from Basement 1 and ending on It Lives!. Once the player defeats those 8, the 9th room will contain some random assortment of items, and finally the 10th room will contain Sandman himself

Health: 8,000 (Has Damage Resistance)
Found: Polaroid
Room: 1×1* (x2)

Pattern:
Sandman’s fight takes place over 2 separate 1×1 rooms, though all are counted as a single boss fight. The general room layout has Sandman at the top-centre of the room, looming over a pit. The pit has a smokey effect within it.
Phase 1:
-May disappear into the darkness, before a skeletal hand reaches out towards the player. Afterwards it will sink back into the dark, with the Sandman appearing again

(Damage)
-May create 8 arcs consisting of 12 projectiles each that all move in a wiggle worm-esque fashion

(Damage)
-May launch 8 projectiles at the player directly that all have varying ranges, causing them to fall at different times. Each one also has a Cricket’s Body effect where they will split into smaller projectiles upon landing

(Damage)

(Damage, Split Shots)
-May launch 2 brimstone lasers that intertwine in a double-helix

(Damage)
-May launch several ipecac shots in 2 streams. Both streams of shots start directly downward before both are rotated 90 degrees in opposite directions. Additionally, the shots leave creep where they land

(Damage)

(Damage, Creep)
-May disappear into the darkness before summoning several skeletal hands to drop from the ceiling, similar to Mom’s Dead Hand(s). However, unlike the enemy, these cannot be killed and simply despawn after retreating back upward, with Sandman re-appearing once they all leave

(Damage)

(Damage, Rock Waves)
-May create 4 Ludovico-like projectiles in the corners of the room. They will move towards the player, but will also mimic the player’s movement inputs to a degree. They eventually despawn on their own

(Damage)
-Shoots 3 streams of grey shots that gradually rotate clockwise. If one reaches the corner of the room it will be moved to the other side and continue being fired

(Damage)
-May launch several large grey shots that rush across the room either horizontally or vertically a short time after appearing. As they move they spawn stationary smaller projectiles

(Damage)

(Damage, Smaller Shots)
Once 3,500 of its health is removed, it will retreat into the darkness. A door will spawn behind it, and the room the player is currently in will begin collapsing. The player has to go through the door to continue the fight, or falling into the pits as the room collapses (which still happens even with flight) will damage the player by a heart before teleporting them into the next room regardless

Boss 18 – Sandman (Continued)

Phase 2:
Sandman becomes more aggressive, enhancing some of its previous attacks alongside gaining new ones.
The arena, while technically the same in functionality, now looks closer to the Dark Room; without visible walls and instead having a smokey void in their place (though it still hinders movement as a wall would)
-The ‘skeletal grab’ attack is mostly the same, but releases a burst of 16 shots in all directions upon stopping

(Damage)

(Damage, Shots)
-The ‘wiggle worm’ attack is mostly the same, but now consists of 12 arc in total and the ‘wiggle’ effect becomes more intense with each subsequent arc

(Damage)
-The ‘splash damage’ attack no longer launches projectiles, but instead launches a brimstone laser that releases projectiles to its left and right as it is fired

(Damage)

(Damage, Shots)
-The ‘helix brimstone’ attack has a wider arc and is faster, and also creates 2 other lasers that travel horizontally at the bottom of the room

(Damage)
-The ‘ipecac’ attack is the same mostly, but Sandman will also independently launch ipecac shots directly at the player as well roughly every half-second that also leave creep

(Damage)

(Damage, Creep)
-The ‘skeletal hand’ attack’s hands look the same, but replace the rock waves with brimstone lasers launched in the cardinal directions. Also, only a maximum of 5 are summoned

(Damage)

(Damage, Brimstone)
-The ‘ludovico’ attack now summons a single brimstone laser ring at the centre of the room that chases the player. It periodically releases 6 shots out in bursts, and upon disappearing leaves a single small ring of creep

(Damage)

(Damage, Shots)

(Damage, Creep)
-The ‘3 stream’ attack is almost entirely different. It launches 8 brimstone lasers, all spaced-out evenly, and once they fade launches a new barrage of 8 more at a slightly different angle, and finally another 8 once they fade. These 3 ‘waves’ of lasers ultimately cover the entire arena

(Damage)
-The ‘grey shot rush’ attack is mostly the same, but has more larger projectiles than before

(Damage)

(Damage, Small Shots)
-The first new attack has Sandman disappear, only for several smaller Sandman enemies to appear from the unreachable void beyond the arena’s platform. Similar to Red Ghosts, these mini-Sandmen all appear and promptly fire brimstone lasers before disappearing. Once all of them are finished firing, the larger Sandman reforms

(Damage)
-It may summon a spiralling grey orb in the middle of the room, similar to an anti-gravity brimstone shot. It then launches a brimstone laser at the player, which will then begin to rotate around the room. It usually rotates around 720 degrees, lingering until Sandman’s next attack begins, before disappearing

(Damage)

(Damage, Orb)
-Sandman may roar, causing several brimstone lasers to be launched diagonally across the arena in a fixed, mesh-like pattern

(Damage)
–There is also a variant where the lasers launched are directly vertical and/or horizontal, but retain the mesh-like pattern

(Damage)
Once Sandman’s health is depleted, it will shriek before disappearing into a blinding light. In the aftermath, it spawns a large wall-sized portal with a white noise-like effect within that can be entered to see Sandman’s special ending, as well as a Void portal 100% of the time in the centre of the room

Champion Variants:
[None]

Extra Info:
-The ending tied to Sandman is Isaac waking up for a dream, with Mom simply asleep in the arm chair in another room, and the general idea that most of the game was just a dream
-Sandman’s concept was partially inspired by the ‘dream theory’, a fairly common theory used to explain certain otherwise hard-to-explain aspects of lore or story by simply saying that it was a dream and that nothing ever happened, hence the ending
-Instantly killing Sandman is impossible, similar to the Golden Door’s boss, as technically it is made of 2 different entities due to the room transition halfway through the fight. Therefore, with the Chaos Card, it is best to save it for the harder 2nd phase
-There is a special character, called the Dreamer, planned to be unlocked if the player defeats Sandman and travels through the large portal
-Sandman had a few different names during development, including The Dreamer and Nightmare, with the former being dropped due to sharing the name with the planned character, and the latter simply being dropped in favour of Sandman
-In terms of difficulty, Sandman is placed roughly between ???’s boss and Void’s boss, which fits its stage placement being roughly between the two
[Added: 26/12/20]

[Final Notes]

And that was the end of the Isaac content… or is it?

No, actually, no it’s not. There is another page planned to be on the way, consisting of characters, items, unlocks, and other general additional stuff. It was originally planned to be part of this page, but I decided against it due to the amount of space bosses usually need in my experience with making boss pages

Special thanks to the Isaac team, and the Isaac modders who (despite me not checking out much stuff yet) helped inspire me to try this out.
Also a big shoutout to OmegaFerretMusic, who has been working on TBoI characters for the Technological Terror devs already, but is currently also working on a Tomato mod I got to collab with, so I’m excited to see how it turns out

Anyways, thanks for having a look at this page, hope you enjoyed my attempt at stepping out of Terraria stuff for a bit to try out making content for a different game

Thanks for having a look, hope you enjoyed 🙂

Hope you enjoy the Guide about The Binding of Isaac: Rebirth – TBoI Boss Ideas, if you think we should add extra information or forget something, please let us know via comment below, and we will do our best to fix or update as soon as possible!