Gapers
Gapers are one of the most common enemies of the first chapters. They act by usually chasing Isaac in an attempt to deal contact damage.
More information about Gapers in general can be found in the vanilla page.
Pester
Pesters behave identically to Gapers, but come with an orbiting 
Eternal Fly.
The Eternal Fly will stay attached if the Pester becomes a 
Pacer or 
Gusher on death.
Marge
Marges behave identically to Gapers, but spawn 4-5 
Swarm Flies upon death.
Wick
Wicks chase after Isaac, spawning small extinguishable fires as they take damage.
They will also occasionally spit a larger extinguishable flame at Isaac and will spawn another on death.
Charlie
Charlies are charred Gapers that behave similarly to 
Gurgles.
They will occasionally lob an ashy projectile towards Isaac that deals no damage, but leaves a patch of gunpowder that can be ignited.
Notes
- Charlie can spawn with any of 10 random expressions. This is purely cosmetic however and doesn't change its behavior in any way.
Buckethead
Bucketheads are armored 
Frowning Gapers found in Downpour and Dross. They behave identically and chase at the speed of standard Gapers, but have Boss Armor until their bucket is fully knocked off (an equivalent of about 10 HP). After their bucket is knocked off, they will speed up, now chasing at the pace of Frowning Gapers.
Some Bucketheads will be hiding in overturned bucket grids, only to come rising up once all other enemies have been killed. Hiding Bucketheads can sometimes wiggle a bit before rising up, delaying their chase by a moment.
Notes
- Hidden Bucketheads can be bombed to kill them prematurely.
- Frowning Gapers spawned from destroyed Bucketheads in Dross have a unique appearance, but behave identically.
Fathead
Fatheads pursue Isaac and explode into a large fart cloud on death.
The fart deals no damage, but will knock back both Isaac and other enemies.
Sackboy
Sackboys are sack-like Gapers that slowly follow Isaac, occasionally spitting out a bunch of 
Baby Spiders and 1-2 regular Spiders, as well as spawning more on death.
Sourpatch
Sourpatches will chase Isaac faster than regular Gapers, and will split into their head and body on death.
Sourpatch Head
Sourpatch Heads behave similarly to slower 
Hoppers, jumping about randomly and pursuing Isaac if he draws near. With each hop, they will also leave a small puddle of yellow creep.
They can appear in rooms on their own.
Sourpatch Body
Sourpatch Bodies behave similarly to Gushers, spraying low range projectiles in the direction they're moving. However, they fire much more rapidly than normal Gushers and also move a bit faster.
They can appear in rooms on their own.
Pitcher
Pitchers will chase Isaac, periodically coughing a cluster of tar projectiles towards Isaac which spawns 1-3 
Blots and a pool of black creep upon landing.
Pale Gaper
Pale Gapers are upgraded versions of Gapers that behave nearly identically, chasing after Isaac slightly faster than their counterparts. If Isaac is in line of sight, they will roar, opening their mouth wider and increasing their speed for a period. Afterwards, they will periodically roar as normal Gapers usually do as long as they maintain line of sight with Isaac. Each roar will continuously maintain their speed; only ever occasionally slowing down for a brief moment between roars. Upon death, they transform into a Pale Gusher.
If a Pale Gaper loses line of sight with Isaac, it will return back to its slower speed, and will take a moment after returning to the chase to roar again.
Notes
- In rooms with
Magnifiers, Pale Gapers will transform into Pale Mag Gapers that behave identically to their regular counterpart.
Pale Gusher
Pale Gushers are upgraded variants of Gushers. They behave like normal Gushers, but fire projectiles at a faster rate; when close to Isaac, they will chase after him with the stream of projectiles angled towards Isaac.
Motor Neuron
Motor Neurons are fusion between 
Nerve Endings and Gapers.
They pursue Isaac, and will sometimes spin their nerve around, creating a large damaging radius around themselves and deflecting any tears or bombs that are sent near them.
Curdle
Curdles follow Isaac slowly, leaving behind a trail of red creep. A layer of flesh covers their face that will be knocked off upon death, spawning 1-2 
Leper Flesh and creating a small pool of red creep. Afterwards, they continue on without the flesh and with 25 more HP.
Naked Curdles move faster and leave a shorter-lasting trail of red creep. They behave similarly to Gurgles, occasionally firing a large arcing 
Haemolacria projectile towards Isaac that pops into a cluster of smaller projectiles upon impact. Upon death, they create another small pool of red creep.
Naked Curdles are most commonly spawned by Curdles, but can sometimes be encountered on their own.
Nailhead
Nailheads behave identically to Gapers until they get close to Isaac or take enough damage, after which their head explodes, releasing 8 damaging nails in a ring around it that remain on the ground for an extremely long duration or until the room is cleared.
After their head pops, they will move faster and leave behind a small trail of red creep.
Bub
Bubs are variants of 
Rotten Gapers primarily found in rooms with the Morbus backdrop. Like Rotten Gapers, they exhibit slightly different behavior depending on the appearance of their head.
From left to right, their behaviors are:
- Medium speed, periodically stops and shoots a single arced tooth projectile towards Isaac. Hunched over, resembling a Gurgle.
- Slow speed, periodically spawns a Spider behind itself while chasing Isaac.
- Medium speed, spawns a
Toma Chunk on death. - Fast speed, explodes into a small shower of projectiles and spawns a Spider on death.
- Medium speed, spawns a
Black Globin's Body with a unique coloration on death.
Mag Gaper
Mag Gapers are tainted variants of Gapers found in the 
Ascent. They quickly chase after Isaac if he's in their sight and can destroy any obstacles they run through. If Isaac breaks line of sight with a Mag Gaper, it will wander around randomly.
Trivia
- Marge is a reference to Marge Simpson of the Simpsons television series and her signature hair, resembling the aptly named beehive hairstyle.
- Wick has been completely reworked in Reheated due to the introduction of the
Revenant in Repentance, which behaves almost identically. - Bucketheads are based off of Buckethead Zombies from Plants vs Zombies. The sound used when the bucket is hit is taken from said series.
- Sackboy's name might be a reference to Little Big Planet's protagonist of the same name.
Warheads and Sourpatches are named after each respective brand of sour candy.- Motor Neuron's first appearance was showcased in a Reddit Post by developer HappyHead.
- In the files, in Curdle's folder, a set of various heads can be found. They appear to be placeholder sprites or were used in early versions of Curdle.
- Bub was originally from the unreleased Morbus MOD.
- Its first appearance was showcased in a Reddit Post by developer THX.
- Mag Gapers are a reference to Mag Agents from Madness Combat, which are bigger and stronger versions of Agents.
- Nailheads were added in The Spookaween Update.
- Pale Gapers were added in The Spitshine Update.
- Pale Gushers were added to regular rooms in The Spitshine Update, prior to that update they could only be spawned by
Corrupted Larry as a part of 
Warp Zone boss fight. - Bucketheads have a unique appearance when encountered on the Boiler floor if the Fall from Grace MOD is installed.
Gallery
Various appearances a Charlie can have.
Wick's appearance in Mausoleum.
Buckethead's appearance when it emerges from a bloody bucket.
Buckethead's appearance in Dross.
Buckethead's appearance in Dross, when it emerges from a bloody bucket.
Buckethead's appearance in Dross, in the Peepee backdrop.
Appearance of a Frowning Gaper spawned from a destroyed Buckethead in Dross.
A Pale Gaper's appearance after roaring and while sped up.
A Pale Gaper transformed into a Pale Mag Gaper.
A spinning Motor Neuron.
A Nailhead with its head popped.
The nail left by a Nailhead after its head explodes.
Appearance of a Black Globin's Body spawned by Bub.
Buckethead's appearance in Boiler.
Pester's original appearance in the Afterbirth+ version of Fiend Folio.
Wick's original appearance in the Afterbirth+ version of Fiend Folio.
Placeholder sprite of Pester.
Unused head sprites found in Curdle's folder.
Concept art for Wick.
Concept sprite for Motor Neuron alongside other monster concepts.
Concept art for Nailhead.
Concept sprite for Bub alongside other monster concepts.
