Gapers walk towards Isaac by the most direct route possible. They will actively path around obstacles and other enemies that block their path to Isaac.
They can transform into Pacers or Gushers after dying.
Variations
Frowning Gaper
Frowning Gapers move quicker than Gapers and have closed eye sockets upon spawning, when they have line of sight with Isaac they will be opened and gain extra permanent speed. They have a high chance to turn into Pacers or Gushers upon death.
Flaming Gaper
Flaming Gapers behave identically to regular Gapers, but move at a faster pace, though not as fast as Frowning Gapers.
Unlike other flaming enemies they are not immune to damage from fire sources and regular Gapers will not turn into Flaming Gapers upon contact with any source of fire.
Nulls
Nulls behave similarly to Frowning Gapers, but walk faster and periodically phase in and out of visibility.
Notes
- White Champion Nulls may not be able to turn invisible while invincible.
- They are referred to as "Nulls", which goes both for its singular and plural usage.
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 walk towards Isaac at a faster pace than Gapers but are slower than Frowning Gapers. When they are near Isaac, they fire an 
Ipecac shot at him. These shots will kill other enemies in their Area of Effect, but Gurgles themselves are immune to their own shots. Killing a Gurgle has a chance for it to transform into a Splasher.
Crackle
Crackles are a variant of Gurgles found only in 
Ashpit. 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.
Blue Gaper
Blue Gapers walk towards Isaac slightly faster than Gapers and are mainly spawned during the Hush boss fight.
Notes
- They can rarely appear in Bedrooms and I AM ERROR rooms.
They can rarely appear in a closet in Basement, Depths, and Necropolis.- Blue Gapers can also be found in the unique rooms created by Blue Key and in ??? Red Key rooms.
They can rarely appear in a 
Greed Gaper
Greed Gapers behave identically to Blue Gapers and are spawned during the Ultra Greed boss fight. They have 4 different appearances though this is purely cosmetic. If they do contact damage to Isaac, similar to Keepers, Isaac will lose or drop some coins.
Notes
- 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 Bulbs. They can, however, still appear in certain Super Secret Room layouts. Greed Gapers can also appear in Ultra Secret Rooms.
2-4 Greed Gapers have a chance to appear in Treasure Rooms.
Deep Gaper
Deep Gapers are completely hidden upon spawning and emerge from the floor once all previous enemies on certain room have been killed. Deep Gapers walk towards Isaac slightly faster than 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 initially walk slowly towards Isaac, but after taking damage or getting close to him they will release the liquid stored in its mouth as a chaotic burst of projectiles. After firing their projectiles, they chase Isaac at the speed of Frowning Gapers, attempting to deal contact damage. They have a high chance to turn into Pacers or Gushers upon death.
They will still spit out their projectiles if killed in an instant with high damage, firing towards Isaac even if he is not within targeting range.
Wraith
Wraiths walk towards Isaac slightly faster than Gapers, but are completely invisible and can only be detected 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 chase Isaac but have slightly different behavior depending on their appearance:
- 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 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 
Corpse during the boss fight with Mother. They are an undead version of 
Isaac.
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.
Notes
- Due to Dead Isaac only being encountered via one attack, it is possible to go multiple runs without finding them.
- This can be inconvenient, as Dead Isaac counts as a Bestiary entry.
Twitchy
Twitchies are a Gaper/Trite hybrid that 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 chase Isaac at a pace faster than most Gaper variants but still slower than Frowning Gapers. Upon death they split into a Level 2 Horf, and a Level 2 Gusher. They deal a whole heart of contact damage.
Gallery
- Frowning Gaper 1.png
A Frowning Gaper before It moves close to Isaac.
- Null 1.png
A Nulls before it moves close to Isaac.
A Gaper's appearance in Downpour and Flooded Caves.
A Gaper's appearance in Dross.
A Frowning Gaper's appearance in Downpour and Flooded Caves.
A Frowning Gaper's appearance in Dross.
A Deep Gaper's appearance in Dross.
A Blurb's appearance in Dross.
A Blurb's appearance outside of Dross, Downpour and Flooded Caves.
A Wraith's appearance in Dross.
Slow Rotten Gaper.
Moderate speed Rotten Gaper.
Fast Rotten Gaper.
Small Maggot spawning Rotten Gaper.
Very fast Rotten Gaper.
A Twitchy in Antibirth
Trivia
- When the Head of the Keeper 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 Downpour 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.
A Bugs
 Bug!
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If a Dark-Red champion Frowning Gaper does not become a gusher or pacer and reforms, the head won't appear until the Gaper sees the player. The same goes for a normal Gaper, however, the head won't appear once reformed. |
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| Bug!
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If an  Explosivo tear is stuck to a Null when it becomes invisible, the tear will fall to the ground.
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| Bug!
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Rotten Gapers don't appear in the Bestiary in any form. |
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| Bug!
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 If a Champion Gaper is killed and it turns into a Pacer/Gusher, it will no longer be a champion.
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 The Binding of Isaac: Rebirth
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