Monsters

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 Bestiary, with the exceptions being the Rag Man's Ragling and Suction Pitfall.

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. The champion's coloration/size 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 have a visual 15% size increase, 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. 50% smaller both visually and collision-wise, making them 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. Visually 50% larger, though collision remains the same. 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%

• Champion Belt adds 15% to the base champion chance. This has no effect in The Void.
• Purple Heart doubles the champion chance, and stacks with Champion's Belt.
  • Mom's Box changes Purple Heart to quadruple the chances instead of doubling.

• 

  Concept art for the champion versions of the Nest.

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