Gaper

Gapers are monsters that resemble Isaac but have blood instead of tears, and their skin is paler. Gapers are commonly found in The Basement and The Cellar.

Gapers will walk towards Isaac by the most direct route possible. If there is no way to reach Isaac, due to obstacles such as rocks or poops blocking the way, they will stand still until a proper route is created.

Sometimes they turn into Pacers or Gushers after dying.

Frowning Gaper
Frowning Gapers look identical to regular Gapers, but have empty eye sockets that appear closed before they get close to Isaac. When awake, they have the same head sprite as Horfs. Frowning Gapers move quicker than Gapers, and the chance for them to turn into Pacers or Gushers is higher.

Flaming Gaper
Flaming Gapers behave identically to regular Gapers, though they move at a faster pace, but not as fast as Frowning Gapers. They appear to be on fire, but despite this they aren't negatively affected by it in any way. They mainly replace most of the regular Gapers in the.

Cyclopia
The Cyclopia moves slower than normal Gapers, but leaves behind a short-lasting trail of Red Creep and occasionally fires a blood shot towards Isaac.

Gurgle
Gurgles are considerably tougher enemies that look identical to Frowning Gapers aside from their green coloration, and are very common in. When they get near Isaac, they fire an shot at him. Killing it has a small chance for it to become a Splasher. These shots will kill other enemies in their Area of Effect, but Gurgles themselves are immune to their own shots.

Like other enemies' explosive projectiles, Gurgles' shots can be used to shatter Rocks or open Secret Rooms by making them fire at the appropriate area.

Gurgles are somewhat more predictable and accurate in their shots compared to Guts and Walking Guts, because they will always shoot at Isaac's position. However, the timing of their shots is unpredictable. As such, an effective strategy of delivering explosives to a particular area (e.g. tinted rock or potential Secret Room entrance) is to stand still in that position as long as possible before moving to avoid getting touched, to prompt the Gurgles to shoot their projectiles at you.

In Repentance, Gurgles have a hunched posture, like how they did in the original game.

Crackle
 Crackles  are a variant of Gurgles found only in. They walk towards Isaac similar to a Gurgle, but instead of shooting an explosive shot, they shoot a ball of fire that releases 4 lines of fire in all cardinal directions when it touches the ground.

Nulls
Nulls appear fairly rarely in Chapter 3 and below. They behave similarly to Frowning Gapers, but walk faster and have the ability to phase in and out of visibility.

Blue Gaper
Blue Gapers behave similarly to regular Gapers and are mainly spawned during the Hush boss fight. They can rarely appear in Bedrooms and I AM ERROR rooms.

They can rarely appear in a closet in, , and. Blue Gapers can also be found in the unique rooms created by Blue Key and in  rooms.

Greed Gaper
Greed Gapers behave similarly to regular Gapers and are spawned during the Ultra Greed boss fight.

2 Greed Gapers may rarely replace the shopkeeper in Shops.

2-4 Greed Gapers have a chance to appear in Treasure Rooms.
 * Greed Gapers no longer appear in treasure rooms and are replaced by the Bulb Fly. They can, however, still appear in certain Super Secret Room layouts. Greed Gapers can also appear in Ultra Secret Rooms.

Deep Gaper
Deep Gapers are a new Gaper variant that appear in and. They will emerge from the floor once all previous enemies on certain room have been killed. Deep Gapers behave like normal Gapers after emerging.

This enemy has 14 design variants, 7 for the Downpour floor and 7 for the Dross floor. These variants are purely cosmetic with the exception of one that has a Small Leech sticking on its head, which will detach from it and chase Isaac when the Gaper is killed.

Blurb
Blurbs appear in and, with a different appearance for either environment. They initially walk slowly towards Isaac, but after taking some damage or getting close to him, will release the projectiles stored in its mouth as a chaotic burst of tears. After firing their tears, they act like regular Gapers and chase Isaac faster than before, attempting to deal contact damage. They will still spit out their projectiles if killed in an instant with high damage, firing towards Isaac even if he is not being targeted.

Wraith
Wraiths appear in and  with a different appearance for either environment. They behave like regular Gapers, but are detectable only by their reflections and the ripples they make in the water. The occasional lightning strikes in Downpour will also make them briefly visible.

They are visible in the Mirrored World, but their reflections will be invisible instead, appearing when lightning strikes.

Rotten Gaper
Rotten Gapers are a variant of Gapers found only in. They chase Isaac faster than regular Gapers, and have slightly different behavior depending on their facial expression.
 * If its eyes and mouth are normal, it chases Isaac slowly, at the speed of a regular Gaper. (ID 10.3.4)
 * If it has a flattened eye, it chases Isaac slightly faster, at the speed of a Frowning Gaper. (ID 10.3.1)
 * If it has an empty eye socket, it chases Isaac quickly, slightly slower than a Gazing Globin. (ID 10.3.2)
 * If it has its eyes closed, it chases Isaac slowly, spawning Small Maggots once every two seconds up to a maximum of 6. (ID 10.3.3)
 * If it has its tongue sticking out, it chases Isaac similarly to Lust, gaining speed as it moves but changes directions slowly, losing momentum as it does. This version will also not normally run into Isaac but instead runs around and maintains a distance to his position. (ID 10.3.5)

Dead Isaac
Dead Isaac is a variation of a Gaper that only appears in the during the boss fight with Mother. They are an undead version of.

Mother summons a horde of Dead Isaacs at the bottom of the arena that walk up towards Mother. Once they reach Mother, she swipes at them, killing them, releasing a burst of blood shots, and launching their corpses towards Isaac.

After a while, she ends this attack by slamming down both hands, which causes a small rock wave to appear beneath any remaining Dead Isaacs, launching them up into the air.

Twitchy
Twitchies are a Gaper/Trite hybrid found only in. They alternate between chasing Isaac and rapidly leaping at him. They leap at Isaac 1-3 times before returning to chasing him on foot, and their leaps can target him from almost across an entire normal-sized room. Most leaps target Isaac's location though they will occasionally attempt to leap to where Isaac is moving. They can also occasionally leap away to dodge Isaac's tears.

Their heads also occasionally twitch violently (hence the name), although this is purely cosmetic.

Level 2 Gaper
Level 2 Gapers appear in the. They look like a large, decaying version of Frowning Gapers.

They behave much like Frowning Gapers, however once they take enough damage, they become split into a Level 2 Horf, which spits Small Maggots at Isaac, and a Level 2 Gusher, which runs around the room and spawns Small Maggots.

Trivia

 * When the is picked up as Keeper, he will look similar to the Greed Gaper.
 * The appearance of Cyclopias is reminiscent of the fatal birth defect of the same name, which is characterized by the failure of the embryonic prosencephalon to properly divide the orbit of the eyes into two cavities.
 * A Stoney makes the same sound as a Large Champion Gaper.
 * Frowning Gapers and Nulls don't make noises until they open their eyes and start chasing the player quicker.
 * Greed Gapers are also known as Greedlings, a name given by a card of it from The Binding of Isaac: Four Souls, although it's seldom referred to as a "Greedling" by players.
 * Gapers and Flies are some of the monsters with the most variations. The Gaper has 14 variations.
 * Blurbs spawned outside of will be skin-toned
 * Wraiths spawned in rooms without water will appear translucent.
 * Twitchys in Antibirth have a more melty and greenish appearance than in Repentance.
 * In Antibirth, Deep Gapers were referred to as Tidal Gapers.