Abaddon

Abaddon is an unlockable passive item.

Effects

+1.5 damage.
+0.2 speed
- Also affects maximum speed (may never exceed 2.0).
Removes all current Red Heart containers and grants 6 Black Hearts.
Converts all current Red Heart containers into Black Hearts, and adds 2 additional Black Hearts.
Empties all Bone Hearts without removing them.
Adds a chance to shoot fear tears.
This item belongs to the Leviathan set. Collecting three items from this set will transform Isaac into Leviathan.

Fear tear effect depends on the luck stat, and the formula used to determine the chance is: 15100−⌊Luck⌋
- At base Luck (0), the chance is 15%, maxing out at 100% at 85 Luck.
- Dark Matter is significantly better at inflicting fear than Abaddon.
Does not remove Soul Hearts or Eternal Hearts.
As it removes all Red Heart Containers, other Deals with the Devil can be taken for "free" as long as Abaddon is taken last while still having at least 1 Container.
Can always be taken as a deal. Even if Isaac only has one or two Soul Hearts, the Black Hearts will be granted after taking the item.
Emptied Bone Hearts will not be converted to Black Hearts.

Bethany: Leaves her with half a Red Heart with her other Heart Containers removed.
Greed's Gullet: If heart containers are being granted, removes them as well as 25 cents.
Keeper: Instantly kills him when picked up.
Keeper/ Tainted Keeper: Sets Coin Hearts to 1 on pickup.
Mom's Perfume: The chance to inflict fear does not stack.
Tainted Bethany: Does not remove stored Red Hearts nor converts them into Black Hearts.

In the Hebrew Bible, the name Abaddon is used as a reference to a bottomless pit, often appearing alongside the place of the dead (which is known as Sheol), meaning the land of the dead. The actual Hebrew word Abaddon (אבדון - pronounced avadon) means "doom".
Abaddon is the Hebrew equivalent of Apollyon.
In the New Testament's Book of Revelation, an angel called Abaddon is written as the king of an army of locusts; his name is first transcribed in Greek (Revelation 9:11 – "whose name in Hebrew Abaddon").
Abaddon also shares its name with a level from Edmund's previous game Super Meat Boy.
Lil Abaddon resembles this item's costume and shares a similar name, but its effects are closer to Maw Of The Void.

Bug!	If Keeper picks up Abaddon, it will remove all of his Coin Hearts but will not kill him until he picks up an item. This still applies if Abaddon is acquired via the Debug Console, but not if the item is picked up normally.