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]
(Repentance+) Locusts do more damage from different quality items, 50% of Isaac's damage if a quality 0 item, 75% if quality 1, 100% if quality 2, 150% if quality 3 and 200% if quality 4.
Notes[]
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.
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.
Special Locusts[]
120 Volt / Jacob's Ladder: A pale blue locust with arcs of electricity that deal 0.1 damage per tick.
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.
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 (the same amount of charges in repentance+). Stats and effects of the active items absorbed prior to consuming Abyss are kept and will trigger every time Void will be used.
In-game Footage[]
Trivia[]
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.
Bugs[]
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.
References[]
↑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.
Shop or the 
Bug!
Ipecac locusts are supposed to explode. This never happens in game; Ipecac only gives a locust that deals slightly more damage and poisons enemies.
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.
Tainted Apollyon Unlocks 
Delirium Unlocks 
The Binding of Isaac: Rebirth
