Gaper

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

Gapers will attempt to walk towards Isaac by taking the most direct route possible. If there is no way to reach Isaac, due to obstacles such as Rocks or Poop blocking the way, they will stand still and avoid moving towards Isaac until a proper route is created.

On occasion, they can turn into Pacers or Gushers after dying.

Variations

Frowning Gaper

Template:MonsterTable Frowning Gapers look identical to regular Gapers, but have empty eye sockets that appear closed before they get close to Isaac. When awoken, they have the same head sprite as Horfs. Frowning Gapers move quicker than Gapers and spawn Pacers and Gushers more often.

Gurgle

Template:MonsterTable Gurgles are enemies that look identical to Frowning Gapers. They are green and have at least quadruple the health of a normal Gaper. When they get near Isaac, they shoot an Ipecac shot at him. Killing it has a small chance for it to become a Splasher.

They shoot Ipecac shots at Isaac at very short range. 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 Gurgles 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, in order to prompt the Gurgles to shoot their projectiles at you.

Skinny

Template:MonsterTable Skinnies are a version of the Gaper with melted faces and a very small creep trail behind them. Skinnies travel much slower than normal Gapers, making them easy to kill without receiving damage. If you have a flying ability and hide inside a rock, they will stop moving.

Rotty

Template:MonsterTable Skinnies are replaced by Rotties in the Depths and below. They still leave creep and can turn into Bonys or several Flies after being killed.

Null (Invisible Demon)

Template:MonsterTable Invisible demons appear fairly rarely in the Depths and below. They behave similarly to Frowning Gapers, but walk faster and have the ability to phase in and out of visibility.

(Due to them being referred as "Null" on the game files, their name has led to some confusion. In computer programming so stands NULL for an uninitialized, undefined, empty, or meaningless value.)