Abyss

Abyss is an unlockable activated item added in The Binding of Isaac: Repentance.

Effects

On use, destroys all items on item pedestals in the room and gives a unique red locust familiar for each item destroyed.
- These locusts are permanent once created, up to a maximum of 64, after which creating more will replace older locusts.
  - This limit is shared with Blue Flies and Spiders.
- The locusts loosely follow Isaac similarly to regular Blue Flies, charging in the direction Isaac is firing until hitting an enemy, wall, or certain obstacles like key blocks, dealing Isaac's damage per tick (2-3 times per hit).
- The locusts may gain additional effects depending on the item destroyed.^[1]

Using Abyss in the Shop or the Devil Room will not give you any locusts nor destroy any items that have not been purchased.
In rooms where there are multiple items to choose from, using Abyss will give only one locust for each item choice/set.
If already at the maximum amount of locusts and presented with multiple non-choice item pedestals, using Abyss will only consume half of the pedestals.
Tainted Apollyon starts with this item in the consumable slot.
If Abyss is used while Isaac is holding an item above his head, it can still consume the item and grant a locust.
- This mechanic can be used to destroy bought items, unwanted blind items as well as familiars given by Soul of Lilith.
Using Abyss to destroy items in Boss Rush or Challenge Room counts as taking an item and causes waves of bosses or enemies to start spawning.
Locusts granted by Abyss are not taken away during the sequence to obtain the Knife Piece 2. Mother's Shadow cannot be harmed, but they can help destroy Fire Places blocking the path faster.
Locusts granted by Abyss are nearly irremovable, only Genesis can completely remove all locusts from a character. Sacrificial Altar and exceeding the familiar limit can remove some locusts. Reroll effects such as D4, Tainted Eden taking damage, Missing No., etc. cannot remove locusts.
In Repentance Co-Op if a player dies, any of the special locusts they have will persist, following and attacking from their ghost.

120 Volt / Jacob's Ladder: A pale blue locust with arcs of electricity that deal 0.1 damage per tick.
Blood of the Martyr: A red locust that deals double damage.
Brimstone: A gray, larger locust that is otherwise normal.
The Common Cold / Scorpio / The Virus: A green locust that poisons enemies.
Cricket's Head: A red locust that is larger and deals triple damage.
Fire Mind: An orange, burning locust that sets enemies on fire.
Halo of Flies: Two gray locusts that deal half damage.
Holy Light: A cyan, glowing locust that occasionally calls down beams of light onto enemies they hit that deal 3x Isaac's damage.
The Inner Eye: Three normal locusts.
Ipecac: A large, slow, green locust that deals x1.5 Isaac's damage and poisons enemies.
Mutant Spider: Four normal locusts.
Number One: A yellow locust that is faster, deals damage quicker, but has shorter range.
Spoon Bender: A purple locust that targets and homes in on enemies.

BFFS! / Hive Mind: Increases the locusts' size and damage by 25%.
- These two items don't stack.
Book of Virtues: Spawns wisps in the middle ring in the form of black-glowing flies with extra HP that do not fire tears.
Extension Cord: Electricity will flow between Isaac and the locusts.
Guppy : Damage dealt by locusts can spawn blue flies.
Ipecac: Locusts gain a flat +2 damage.
Tainted Eden: Abyss can be rerolled, but the locusts are permanent.

Baby-Bender / Box of Friends: Does not affect locusts.
Car Battery: No effect.
Death Certificate: Only allows the consumption of one item per Death Certificate room and the consumed item is treated as if it was picked up causing all other items in the room to disappear and forcing Isaac to leave the area.
Genesis: The locusts created by Abyss are removed without creating items to replace them.
Sacrificial Altar: Locusts can be sacrificed for items.
Void: If Void consumes Abyss, the latter will take priority and using Void to consume another item pedestal will generate a locust. Even consuming active items will generate a locust, and Void will not copy that active item's effect. This essentially causes Void to act identically to Abyss, albeit requiring 2 more charges per use. Stats and effects of the active items absorbed prior to consuming Abyss are kept and will trigger everytime Void will be used.

The way that Abyss works is similar to how it's described in the Book of Revelation, where locusts emerge from the Abyss and are controlled by Apollyon.
The swirl in Void's appearance is in the opposite direction of Abyss's.

Bug!	According to `locusts.xml`, Ipecac locusts are supposed to explode. This never happens in game; Ipecac only gives a locust that deals slightly more damage and poisons enemies.

Bug!	Each use of Glowing Hourglass that does not move Isaac to a different room than the one he is currently in (such as the starting room of a new floor) will duplicate the locusts.

↑ Unique locusts and the items that give them are defined in locusts.xml. Every passive item in the game is listed in the file, but only the items mentioned actually have their locusts implemented.