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Monsters refers to the many antagonistic creatures the player will encounter throughout the game.

Most monsters (with few exceptions) will damage Isaac by either touching him or shooting him with projectiles. Less frequently, monsters will spawn additional, lesser monsters, spread creep, or attempt to affect the player's movement. Along with the more common variety of monsters, champion versions can be found lurking about. These monsters are often like their common counterparts, but have a color tint or size change and drop basic pickups on death. There are also champion versions of most bosses.

There are 196 naturally spawning monsters in total. 40 of them were added in Afterbirth and 21 were added in Afterbirth † (13 were added in Booster Packs). Almost all of these naturally spawning entities are featured in the Added in Afterbirth † Bestiary, with the exceptions being the Rag Man's Ragling and Suction Pitfall.

Contents

Monster List

Monster Description
Frowning Gaper
 
Walks towards Isaac, dealing contact damage. Upon getting near Isaac, it will open its eyes and pursue Isaac faster. Usually turns into a Pacer or a Gusher upon death.
Gaper
 
Walks towards Isaac, dealing contact damage. Usually turns into a Pacer or a Gusher upon death.
Flaming Gaper
 
Walks towards Isaac, dealing contact damage. Usually turns into a Pacer or a Gusher upon death.
Gusher
 
Walks aimlessly around the room, occasionally firing a short ranged blood shot.
Pacer
 
Walks aimlessly around the room.
Horf
 
Stationary enemy that fires a medium-ranged blood shot at Isaac when he gets in range of them.
Fly
 
Tiny black fly with neutral AI. Does not hurt Isaac upon touch.
Pooter
 
Slow-moving fly that occasionally fires single blood shots at Isaac. Does not deal touch damage.
Super Pooter
 
An alternate version of the Pooter that fires 2 shots in a V-formation and does not deal touch damage.
Clotty
 
Randomly wanders around the room, firing 4 blood shots in the cardinal directions.
Clot
 
Randomly wanders around the room, firing 4 tar shots in the ordinal directions.
I.Blob
 
Randomly wanders around the room, firing 8 shots in all directions.
Mulligan
 
Walks around the room, avoiding Isaac. Upon death, spawns several flies, which can be Flies, Attack Flies or Pooters. Can suicide to explode and launch four projectiles in the cardinal directions while still releasing flies.
Mulligoon
 
Walks around the room, avoiding Isaac. Upon death, spawns a Troll Bomb and fires four shots in the ordinal directions. Can suicide to explode, spawn a Troll bomb, and launch eight projectiles in all directions.
Mulliboom
 
Chases Isaac and explodes upon death or upon touching Isaac. The explosion deals a half-heart of damage instead of the regular full heart.
Attack Fly
 
Red fly that follows Isaac and deals touch damage.
Maggot
 
Aimlessly moves around the room, dealing contact damage.
Hive
 
Walks around the room, avoiding Isaac while spawning Attack Flies. Spawns a large number of flies upon death, which can be Flies, Attack Flies or Pooters.
Drowned Hive
 
Walks around the room, avoiding Isaac while spawning Drowned Chargers. Spawns a Drowned Charger upon death.
Charger
 
Slowly moves around the room, charging at Isaac when he gets in its line of sight.
Drowned Charger
 
Slowly moves around the room, charging at Isaac when he gets in its line of sight. Explodes into four blood shots in the ordinal directions upon death.
Dank Charger
 
Slowly moves around the room, charging at Isaac very rapidly when he gets in its line of sight, leaving a trail of slowing Black Creep.
Globin
 
Chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which can be killed. Will regenerate after a short period of time if not killed quickly.
Gazing Globin
 
Quickly chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which will slide away from Isaac and can be killed. Will regenerate after a short period of time if not killed quickly.
Dank Globin
 
Chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, spawns a Spider, and leaves a puddle of slowing Black Creep. Will regenerate after a short time if not killed quickly. Leaves another puddle of Black Creep upon death.
Boom Fly
 
Flies around the room diagonally, dealing touch damage and exploding upon death.
Red Boom Fly
 
Flies around the room diagonally, dealing touch damage and releasing 6 blood shots in all directions upon death.
Drowned Boom Fly
 
Flies around the room diagonally, dealing touch damage. Upon death, explodes and fires four blood shots in the cardinal directions. High chance to spawn a Drowned Charger upon death.
Maw
 
Slowly floats towards Isaac, firing blood shots at him when he is in their range.
Red Maw
 
Floats towards Isaac and releases 4 blood shots in the cardinal directions upon death.
Psychic Maw
 
Slowly floats towards Isaac, firing homing shots at him when he is in their range. Spawns with an Eternal Fly orbiting around it.
Host
 
Stationary enemy that is normally invulnerable. Raises its head up when Isaac gets close, revealing a fleshy stem that can be damaged. Upon raising its head, it will fire 3 blood shots in a spread and lower its head again.
Red Host
 
Stationary enemy that can be damaged even when its head is lowered. Fire 5 spread blood shots when it raises its head.
Hopper
 
Slowly hops around the room, doing touch damage. Can turn into a Flaming Hopper by jumping into fire.
Trite
 
Quickly leaps towards Isaac and deals touch damage.
Boil
 
Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires multiple short-ranged blood projectiles in random directions when fully swollen.
Gut
 
Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires Ipecac shots in random directions when fully swollen.
Sack
 
Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Occasionally spawns Spiders when fully swollen.
Spitty
 
Slowly moves around the room, occasionally firing a single blood shot forward.
Brain
 
Slowly crawls around the room, leaving a trail of Red Creep.
Leaper
 
Hops around the room, doing touch damage. Occasionally jumps high into the air, dropping down onto Isaac's position while firing 4 blood shots in the cardinal directions.
Mr. Maw
 
Walks towards Isaac and attacks by launching its head towards him. Turns into a Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
Mr. Red Maw
 
Walks towards Isaac and attacks by launching its head towards him. Turns into a Red Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
Baby
 
Slowly floats towards Isaac and fires a blood shot at him. Occasionally teleports and reappears elsewhere.
Angelic Baby
 
Slowly floats towards Isaac and fires three spread shots. Occasionally teleports and reappears elsewhere.
Vis
 
Randomly wanders around the room. Pauses to charge and fire a Brimstone laser when Isaac gets in its line of sight.
Double Vis
 
Randomly wanders around the room. Pauses to charge and fire a Brimstone laser which fires from both sides when Isaac gets in its line of sight.
Chubber
 
Randomly wanders around the room. Pauses to fire a Charger that deals one heart of damage when Isaac gets in its line of sight. The Charger is invulnerable, blocks Isaac's tears, has limited range, and flies back to the Chubber.
Scarred Double Vis
 
Randomly wanders around the room. Pauses to charge and fire a Brimstone laser which fires from all four cardinal sides when Isaac gets in its line of sight.
Guts
 
Attaches itself to a wall or obstacle and rolls around it.
Scarred Guts
 
Attaches itself to a wall or obstacle and rolls around it, leaving a trail of damaging Red Creep.
Knight
 
Moves erratically around the room and charges towards Isaac when in line of sight. Can only be damaged from behind.
Selfless Knight
 
Moves erratically around the room and charges towards Isaac very quickly when in line of sight. Can only be damaged from behind.
Stone Grimace
 
Stationary and invulnerable monster that occasionally fires a blood shot at Isaac. Stops firing when room is cleared.
Vomit Grimace
 
Stationary and invulnerable monster that occasionally fires an Ipecac shot at Isaac. Stops firing when room is cleared.
Poky
 
Slides around the room aimlessly, damaging Isaac by contact. Disappears when the room is cleared.
Slide
 
Quickly slides towards Isaac when he gets in its line of sight, then moves slowly back to its original position. Cannot be destroyed.
Dople
 
Mirrors Isaac's movements and fires blood shots at the same time as Isaac. Can be damaged by spikes.
Evil Twin
 
Mirrors Isaac's movements and fires three spread blood shots at the same time as Isaac. Can fly over obstacles.
Flaming Hopper
 
Quickly hops around the room, doing touch damage. Covers a larger distance than the regular Hopper.
Leech
 
Quickly charges towards Isaac when he gets in its line of sight.
Kamikaze Leech
 
Quickly charges towards Isaac when he gets in its line of sight. Explodes upon death.
Holy Leech
 
Quickly charges towards Isaac when he gets in its line of sight. Explodes upon death. Spawns with an Eternal Fly circling it, which instantly dies when the Holy Leech explodes.
Lump
 
Fires 3 spread blood shots at Isaac when he gets in its line of sight. Will burrow underground and reappear elsewhere after firing.
MemBrain
 
Slowly moves around the room, occasionally hopping and firing 8 large blood shots in all directions. Splits into 2 Brains upon death.
Mama Guts
 
Slowly moves around the room, occasionally hopping and firing 8 large blood shots in all directions. Splits into 2 Guts upon death.
Para-Bite
 
Moves towards Isaac, dealing contact damage. Can burrow underground and reappear elsewhere.
Scarred Para-Bite
 
Moves towards Isaac, dealing contact damage and firing a short-range blood shot at him. Can burrow underground and reappear elsewhere.
Fred
 
Hops out of the ground and burrows elsewhere, firing 4 blood shots in the ordinal directions. Occasionally fires red Ipecac shots at Isaac.
Eye
 
Slowly turns towards Isaac and fires a Technology laser at Isaac if he stands still or is too slow.
Bloodshot Eye
 
Slowly turns towards Isaac and fires a Brimstone beam at Isaac if he stands still or is too slow.
Sucker
 
Flies slowly towards Isaac, exploding into 4 shots in the cardinal directions upon death.
Spit
 
Flies slowly towards Isaac, firing an Ipecac shot towards Isaac upon death.
Soul Sucker
 
Flies slowly towards Isaac. Spawns a vortex that fires four Brimstone beams in the cardinal directions upon death.
Death Scythe
 
Stays stationary for a few seconds, then homes in on Isaac.
Embryo
 
Aimlessly hops around the room, dealing contact damage.
Moter
 
Follows Isaac, similar to Attack Flies. Splits into 2 Attack Flies upon death.
Spider
 
Erratically moves towards Isaac and deals touch damage.
Keeper
 
Hops around the room, firing 2 blood shots in a V formation at Isaac. Upon damaging Isaac, Isaac drops 2 coins on the ground but loses 3.
Gurgle
 
Walks towards Isaac, firing Ipecac shots at him. Can turn into a Splasher upon death.
Walking Boil
 
Does not shrink or regenerate. Walks around aimlessly and fires multiple short-ranged blood projectiles in random directions.
Walking Gut
 
Does not shrink or regenerate. Walks around aimlessly and fires Ipecac shots in random directions.
Walking Sack
 
Does not shrink or regenerate. Walks around aimlessly and occasionally spawns Spiders.
Buttlicker
 
Can start Attached to other Buttlickers and erratically moves around the room, similar to Larry Jr..
Hanger
 
Floats around the room, firing 3 spread blood shots at Isaac. Upon damaging Isaac, Isaac drops 2 coins on the ground but loses 3. Spawns with an Eternal Fly circling around it.
Swarmer
 
Slowly floats around the room, spawning several Attack Flies. Spawns Pooters upon taking damage. Spawns a Boom Fly upon death.
Mask + Heart
 
The Mask is invulnerable and moves around erratically, charging at Isaac when he lines up with it. The Heart avoids Isaac and fires 4 blood shots in the cardinal directions when Isaac gets near. Killing the Heart will automatically kill the Mask.
Big Spider
 
Erratically moves towards Isaac and deals touch damage. Splits into two Spiders upon death.
Eternal Fly
 
Invulnerable fly that circles Corny Poop and various monsters. Turns into a vulnerable Attack Fly after the object or monster it circles is destroyed.
Stone Eye
 
Stationary and invulnerable monster that constantly rotates and fires a flickering Technology laser. Stops firing when the room is cleared.
Constant Stone Shooter
 
Stationary and invulnerable monster that continuously fires shots in a single direction.
Cross Stone Shooter
 
Stationary and invulnerable monster that continuously fires shots in four directions, alternating between cardinal and ordinal.
Brimstone Head
 
Stationary and invulnerable monster that fires Brimstone beams in a specific direction.
Mobile Host
 
Acts like the Host, but follows Isaac and deals contact damage.
Nest
 
Walks around the room, avoiding Isaac while spawning Spiders. Spawns a Big Spider or a Trite upon death.
Baby Long Legs
 
Runs away from Isaac and frequently spawns Spiders.
Small Baby Long Legs
 
Runs away from Isaac and occasionally spawns Sacks.
Crazy Long Legs
 
Chases Isaac, dealing touch damage. Occasionally stops to spit 8 blood shots in all directions.
Small Crazy Long Legs
 
Chases Isaac, dealing touch damage. Occasionally stops to spit 4 blood shots in the diagonal directions.
Fatty
 
Slowly walks towards Isaac. Occasionally farts, which pushes Isaac and adjacent enemies away.
Flaming Fatty
 
Slowly walks towards Isaac. Occasionally farts, which pushes Isaac and adjacent enemies away. Has a chance to leave behind a damaging flame upon death.
Fat Sack
 
Slowly walks towards Isaac. Occasionally leaps off-screen and attempts to land on Isaac, leaving a puddle of Red Creep and shooting 6 blood shots in all directions where it lands. Has a chance to turn into a Blubber upon death.
Blubber
 
Walks around aimlessly and randomly spews a cluster of blood shots in all directions. Has a chance to turn into a Half Sack when killed.
Pale Fatty
 
Slowly walks towards Isaac. Occasionally farts and shoots 6 blood shots in all directions. Has a chance to turn into a Blubber upon death.
Half Sack
 
Wanders around aimlessly and leaves a trail of Red Creep.
Death's Head
 
Invulnerable enemy that moves diagonally around the room, dealing contact damage. Dies when the room is cleared.
Dank Death's Head
 
Moves diagonally around the room, dealing contact damage. Needs to be killed to complete the room.
Mom's Hand
 
Falls from the ceiling. If it lands on Isaac, it deals damage and teleports the player back to the spawn room of the floor. Entering a room containing Mom's Hand will warn the player with Mom's laugh.
lvl2 Fly
 
Flies toward Isaac erratically, dealing touch damage.
lvl2 Spider
 
Crawls around the room erratically, following Isaac and dealing touch damage. Can jump small distances.
Swinger
 
Slowly moves towards Isaac as its head swings around its base. Upon death, spawns a Maw or a Globin depending on which part is killed.
Dip
 
Slowly dashes in random directions, dealing contact damage.
Corn
 
Quickly dashes in random directions, dealing contact damage.
Brownie Corn
 
Quickly dashes in random directions, dealing contact damage.
Wall Hugger
 
Moves around the room like Guts, damaging Isaac by contact. Cannot be destroyed.
Wizoob
 
Disappears, then appears near Isaac and spits a cluster of spectral tears at him.
Squirt
 
Dashes towards the player and deals contact damage. Spawns 2 Dips upon death.
Dank Squirt
 
Dashes towards the player and deals contact damage. Spawns 2 Clots upon death.
Cod Worm
 
Stationary enemy that hides in a shell and spews a burst of blood shots if shot at. Only vulnerable when it pops its head out.
Ring Fly
 
Gathers with any other Ring Flies in the room. These flies orbit around themselves while following Isaac.
Dinga
 
Slowly moves around the room, occasionally hopping to spawn Dips or fire 8 Brown shots in all directions. Splits 2 Squirts upon death.
Oob
 
When Isaac lines up with it horizontally, it charges across the room once. When Isaac is not horizontal to it, it spawns Brains.
Black Maw
 
When Isaac lines up with it horizontally, it charges in his direction and then doubles back, charging back to its original position. When Isaac is not horizontal to it, it spawns Leeches. Explodes when it dies.
Skinny
 
Slowly walks towards Isaac, leaving short-lasting Red Creep behind itself.
Rotty
 
Slowly walks towards Isaac, leaving short-lasting Red Creep behind itself. Spawns a Bony or two Attack Flies upon death.
Crispy
 
Slowly walks towards Isaac, but increases in speed as they take damage. Constantly passively takes damage.
Bony
 
Wanders around the room and throws a bone at Isaac when he is in sight.
Homunculus
 
Starts attached to the wall or an   obstacle. After a while, it detaches, shooting 6 blood shots in all directions, leaving a puddle of Red Creep and chasing Isaac. If it dies while still attached, it will still leave a puddle of Red Creep.
Tumor
 
Moves around the room diagonally, occasionally firing 6 blood shots in all directions. Fires more often upon getting damaged.
Camillo Jr.
 
Moves around the room diagonally, occasionally firing Technology lasers towards Isaac. Fires more often upon getting damaged.
Nerve Ending
 
Static enemy which acts as a meat shield.
Nerve Ending 2
 
Static enemy which whips at Isaac if he gets too close.
One Tooth
 
Follows Isaac and periodically dashes towards him when it gets close. Deals contact damage.
Gaping Maw
 
Stationary and invulnerable monster that sucks Isaac towards it, along with Isaac's tears and enemy projectiles.
Broken Gaping Maw
 
Stationary and invulnerable monster that sucks Isaac towards it, along with Isaac's tears and enemy projectiles. Alternates between active and inactive every couple of seconds. Has a stronger attraction power than a regular Gaping Maw.
Gurgling
 
Charges towards Isaac when he lines up with them, leaving a trail of Red Creep and shooting 6 blood shots.
Splasher
 
Walks aimlessly around the room, firing Ipecac shots in random directions.
Grub
 
Erratically moves around the room like Larry Jr. and charges at Isaac when he gets within its line of sight. Spawns Maggots, Chargers, or Spitties upon death, one for each of its segments.
Wall Creep
 
Crawls along walls to try to line up with Isaac and shoots three blood shots in a line.
Rage Creep
 
Slowly crawls along walls to try to line up with Isaac and shoots a Brimstone laser.
Blind Creep
 
Randomly crawls along walls and shoots three spread blood shots.
Conjoined Spitty
 
Slowly moves around the room, occasionally firing a blood shot from both ends of its body.
Round Worm
 
Pops out of the ground in random locations and spits a blood shot at Isaac if he is in sight.
Ragling
 
Quickly leaps towards Isaac and deals touch damage. Randomly shoots two purple shots that orbit around it.
Rag man's Rag Ling
 
Quickly leaps towards Isaac and deals touch damage. Randomly shoots two purple shots that orbit around it.
Flesh Mobile Host
 
Acts like the Red Host, but follows Isaac and deals contact damage.
Psychic Horf
 
Stationary enemy that fires a homing shot at Isaac when he gets in range of them.
Full Fly
 
Flies toward Isaac erratically, dealing touch damage. Releases 6 bullets in all directions upon death.
Ticking Spider
 
Crawls around the room erratically, following Isaac and dealing touch damage. Can jump small distances. Explodes upon death.
Begotten
 
Starts attached to the wall or an   obstacle. After a while, it detaches, firing 6 blood shots in all directions, turning the room dark, becoming invisible and chasing Isaac. Briefly becomes visible upon getting hit.
Null
 
Act like faster Frowning Gapers, and phase in and out of visibility. When Isaac gets near, they open their eyes and pursue Isaac faster.
Psy Tumor
 
Moves around the room diagonally, occasionally firing 6 homing shots in all directions. Fires more often upon getting damaged.
Floating Knight
 
Behaves like the Knight but slower, and can fly over all obstacles.
Night Crawler
 
Pops out of the ground in random locations and fires four short-range shots that spiral outwards if Isaac is in sight.
Tube Worm
 
Pops out of the ground in random locations and fires a long-range spray of arcing shots.
Dart Fly
 
Flies towards Isaac and attempts to mimic his movements. Deals contact damage.
Conjoined Fatty
 
Slowly walks towards Isaac. Occasionally pauses to fart out a line of damaging Green Creep towards Isaac. Chance to turn into a regular Fatty upon death.
Blue Conjoined Fatty
 
Slowly walks towards Isaac and occasionally farts out a homing Ipecac shot at Isaac.
Fat Bat
 
Slowly flies towards Isaac. Tries to align itself diagonally to Isaac and shoots at him when in that alignment.
Imp
 
Slowly drifts towards Isaac, frequently firing 5 blood shots in quick succession towards him. Tries to avoid Isaac's shots and occasionally teleports and reappears elsewhere.
Lil' Haunt
 
Follows Isaac erratically and occasionally shoots a blood shot towards Isaac's destination, predicting his movements.
Roundy
 
Pops out of the ground in random locations, creating a small rock wave. Fires an explosive Ipecac shot at Isaac if he is in sight.
Black Bony
 
Wanders around the room and throws three bones in a row at Isaac when he is in sight. Explodes upon death.
Black Globin
 
Chases Isaac, dealing a full heart of contact damage and spawning Spiders whenever it takes damage. Spawns a Spider, a Black Globin's Head, and a Black Globin's Body upon death.
Black Globin's Head
 
Slides towards Isaac, leaving a trail of damaging Red Creep.
Black Globin's Body
 
Walks aimlessly around the room, occasionally spawning spiders.
Swarm Fly
 
Follows Isaac in large groups and deals contact damage.
Mega Clotty
 
Slowly moves around the room, occasionally hopping and either firing 6 blood shots in all directions, leaving a puddle of Red Creep, or spawning a Clotty or a collapsed Globin. Splits into two Clotties upon death.
Bone Knight
 
Moves erratically around the room, charges toward Isaac when in line of sight, and leaves behind a short-lasting trail of damaging Red Creep. Can only be damaged from behind.
Cyclopia
 
Walks towards Isaac, dealing contact damage and leaving behind a short-lasting trail of damaging Red Creep. Occasionally shoots a blood shot towards Isaac.
Red Ghost
 
Disappears, then reappears near Isaac and fires a brimstone laser.
Flesh Death's Head
 
Moves diagonally around the room, dealing contact damage. Releases 6 blood shots in all directions upon death. Can be killed, but also dies when the room is cleared.
Mom's Dead Hand
 
Falls from the ceiling. Upon landing, it spawns several rock waves that travel outwards. Spawns several spiders upon death. Entering a room containing Mom's Dead Hand will warn the player with Mom's laugh.
Dukie
 
Flies around the room diagonally, occasionally spitting out 1-2 Dart Flies.
Ulcer
 
Pops out of the ground in random locations and spawns a Dart Fly if Isaac is in sight. Fires a blood shot after spawning 6 Dart Flies.
Meatball
 
Slides around the room. If Isaac is in sight, it will stop to spew a fountain of short-range blood shots in all directions or to spit a line of damaging Red Creep towards Isaac. Spawns a Host upon death.
Pitfall
 
Invulnerable and stationary enemy which Isaac falls into when walked over, taking damage and popping back out after a short delay.
Teleport Pitfall
 
Invulnerable and stationary enemy which Isaac falls into when walked over, taking damage and popping back out at a random location after a short delay.
Suction Pitfall
 
Invulnerable and stationary enemy which sucks Isaac towards itself. Isaac falls into it when walked over, taking damage and popping back out after a short delay.
Ultra Greed Coin (Spinner)
 
Spins around the room, dealing contact damage.
Ultra Greed Coin (Key)
 
Spins on itself and opens a golden door around the room if not destroyed.
Ultra Greed Coin (Bomb)
 
Spins on itself and explodes with a large radius if not destroyed.
Ultra Greed Coin (Heart)
 
Spins on itself and heals Ultra Greed for 13.125 HP each if not destroyed.
Corn Mine
 
Goes off when destroyed or after some time, then releases a cloud of poisonous gas and fires corny shots in eight directions.
Hush Fly
 
Gathers with other Hush Flies and flies towards Isaac in certain patterns. Can also orbit Hush.
Blue Gaper
 
Walks towards Isaac, dealing contact damage.
Blue Boil
 
Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires 1-3 blood shots towards Isaac when fully swollen.
Greed Gaper
 
Walks towards Isaac, dealing contact damage.
Mushroom
 
Stationary enemy that occasionally pops up and fires four shots in the cardinal or diagonal directions. Takes less damage while its head is down.
Poison Mind
 
Slowly crawls around the room diagonally, leaving a trail of Green Creep.
Stoney
 
Chases Isaac and blocks tears, but does not deal contact damage. Temporarily pauses in exhaustion after a certain amount of time. Invulnerable; dies when the room is cleared.
Cross Stoney
 
Chases Isaac and shoots 4 tears vertically and diagonally like a Cross Grimace. Dies when the room is cleared.
Only appears in Aprils Fool (challenge #32) as replacements to regular Stoneys.
Blister
 
Slowly hops towards Isaac, occasionally spawning a Dark Ball. Spawns a Sack upon death.
The Thing
 
Crawls along a wall and attempts to line up with Isaac, then spits a line of damaging Red Creep.
Ministro
 
Hops towards Isaac, occasionally spitting out a cluster of disorganized shots.
Portal
 
Spawns various enemies from the current floor until it either vanishes or is killed.
Tar Boy
 
Fires a short-ranged spray of shots that leave behind slowing Black Creep. Occasionally burrows underground and reappears under any pools of black creep in the room. If Isaac stands on the Creep, the Tar Boy can fire shots straight upwards out of the Creep underneath Isaac.
Fistuloid
 
Flies towards Isaac in an erratic waving motion, periodically firing a blood shot towards Isaac that also knocks itself back. Upon death, fires a worm that flies off screen.
Gush
 
Stationary, harmless enemy that continually creates slowing black creep.
Leper
 
Walks around the room, chasing Isaac but running way if they take damage. Releases a Leper Flesh for every 15 damage taken. After being reduced to 15 health, chases Isaac continously and leaves damaging Red Creep. Spawns a Leper Flesh and a Grey-coloured Gusher upon death.
Leper Flesh
 
Moves erratically and chases Isaac. Fires a blood shot at Isaac upon death.
Mr. Mine
 
Can only appear in pits. Attempts to launch itself at Isaac if he comes near. Occasionally burrows and pops up in another pit, and fires six shots in all directions upon death.
Dark Ball
 
Floats towards Isaac, doing contact damage.
Purple Ball
 
Floats towards Isaac, doing contact damage.

Champions

Some monsters can spawn as a Champion which deviates in coloration and size from its more common form. The champion's coloration denotes which peculiar behaviors and traits it will exhibit. Champions will generally drop a pickup (coinciding with the color of the champion) when killed on normal difficulty. However, in hard mode, the drop rate is reduced to 33%, while in Greed Mode, champions won't drop pickups at all.

Most champions inflict full heart damage regardless of chapter and have double the health of a normal monster. Champions are generally regarded as more dangerous than common monsters.

  Champions always deal contact damage, regardless of what monster they are (e.g. a common Mulligan will not deal contact damage, but champion versions will).

The identifying scheme for champion qualities is as follows:

ID Appearance Effect Drop
0  
Vivid Red
×2.5 amount of HP. Heart
1  
Dark Yellow
Increased movement speed. Little battery
2  
Strong Lime Green
Leaves green creep as it walks. Pill
3  
Vivid Orange
Attacks cause you to drop coins (like Greed or a Hanger). The number of coins dropped range from 1-3, which take away 2-4 coins in total respectively. No coins are dropped if you don't have any. Coin
4  
Vivid Blue
Decreased speed. 3 Blue Flies
5  
Dark Cyan
Explodes when killed. Bomb
6  
White
Invincible until all other enemies are killed. Eternal Heart
7  
Dark Gray
2/3 health, decreased speed. Key
8  
Transparent White
Tears become spectral tears, and it can move past environmental obstacles (such as pits) that it otherwise couldn't when forced. Locked Chest
9  
Black
Fades in and out of visibility, like a Null. Red Chest
10  
Pure Magenta
Periodically shoots short-ranged blood shots, similar to Gushers. Nothing
11  
Mostly Pure Violet
Pulls Isaac and his shots towards itself, like a Gaping Maw. Random trinket
12  
Dark Red
Collapses into a flesh pile upon death and regenerates if not finished off (like a Globin). Double Heart
13  
Very Light Blue
Releases blood shots in 8 directions when killed. 1/2 heart
14  
  Camouflage
The enemy blends into the background and briefly becomes visible when damaged. Rune
15  
  Pulsing Strong Lime Green
Splits into two copies of itself upon death. 2 normal versions of itself
16  
  Pulsing Dark Gray
Repels Isaac's shots when it pulses. Nothing
17  
  Light White
Has 1-2 Eternal Flies circling it. Spawns another fly upon death. Attack Fly
18  
  Small
Decreased health, increased speed and pitch of sound effects. Smaller and more difficult to hit. One Makes You Small pill at 1/5th of difficulty based drop rate; can change other pills in the current rotation.
19  
  Large
Increased health, slightly decreased speed and decreased pitch of sound effects. Larger and easier to hit. Deals two full hearts of damage. One Makes You Larger pill at 1/5th of difficulty based drop rate; can change other pills in the current rotation.
20  
  Pulsing Vivid Red
All other enemies in the room regenerate health at the rate of 20 HP per second while this enemy is alive. Heart
21  
  Pulsating
Spawns an Attack Fly on hit. After each hit, there is a delay until the next hit results in another Attack Fly. A single Pulsating enemy can have up to 5 Attack Flies at once. 4-6 Blue Flies
22  
  Crown
Increased health. All enemies in the room that are not champions will turn yellow while the crowned enemy is alive. The affected enemies will drop batteries like yellow champions upon dying, but otherwise have no extra health, speed or damage 2-3 random pickups
23  
  Skull
Produces a   The Necronomicon effect upon death. Deals two full hearts of damage.   The Necronomicon effect

The chances for Champion monsters to appear are noted in the table below:

Modifiers Normal mode Hard mode   The Void
Base chance 5% 20% 75%
  Champion Belt 20% 35% 75%
  Purple Heart 10% 40% 100%
  Purple Heart +    Mom's Box 20% 80% 100%
  Champion Belt +   Purple Heart 40% 70% 100%
  Champion Belt +   Purple Heart +    Mom's Box 80% 100% 100%

Monster Replacements

Some monsters have a chance to be replaced with other monsters when they spawn,   but only at room entry.   Some replacements only occur on certain floors.

(Disclaimer: Chances are approximate!)

Base Monster Replacement Chance Notes
Rebirth
    10%
    1%
 
    6%
    6%
    5%
    5%
    5%
    1%
 
    10%
    1%
 
    10%
    6%
    1%
 
    10%
    10%
    5%
    1%
 
    6%
    10%
    6%
    6%
    1%
 
    6%
    1%
 
    6%
    6%
  Afterbirth
    60% Exclusive to   Burning Basement
 
    60% Exclusive to   Burning Basement
Only a single Burning Basement room contains a Pale Fatty, making it a very unusual replacement to witness.
 
    60% Exclusive to   Burning Basement
 
    50% Exclusive to   Flooded Caves
    50% Exclusive to   Flooded Caves
 
 
    50% Exclusive to   Flooded Caves
 
    50% Exclusive to   Dank Depths
    50% Exclusive to   Dank Depths
    50% Exclusive to   Dank Depths
 
    50% Exclusive to   Scarred Womb
    50% Exclusive to   Scarred Womb
    50% Exclusive to   Scarred Womb
 
  Afterbirth+
    10%
  20%
    20%
 
    20%
 
    20%
    20%
    10%
    20%
 
 
    20%
    40% Exclusive to   Burning Basement
Rottys do not appear in any Burning Basement room layouts, but can still be replaced regardless.
 
    50% Exclusive to   Flooded Caves
Dank Chargers do not appear in any Flooded Caves room layouts, but can still be replaced regardless.
    20% Exclusive to Aprils Fool challenge


  The Binding of Isaac: Rebirth  
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