Athame

Effect

When Isaac takes damage, a black ring briefly appears around him, dealing tear damage at a rapid rate to everything touching it.
- (Removed in Repentance) When an enemy is killed with the black ring, there is a 15% chance for it to drop a Black Heart.
  - (Added in Repentance) Athame no longer has a chance to spawn black hearts upon killing enemies with the black ring.
- (Removed in Repentance) Black Hearts will drop as soon as the enemy is killed. (In other words, the heart will drop at the beginning of the death animation rather than at the end of the death animation.)

The ring is similar in appearance to the combination of The Ludovico Technique and Brimstone.
It is identical to the ring created by Maw of the Void.
(Removed in Repentance) Especially effective against Envy and Super Envy. Each piece of Envy grants a 15% chance for a Black Heart. It is also effective against Brownie due to all the Brownie Corns it spawns.

Homing tears: The black ring becomes homing, curving around to hit enemies.
Ipecac: Massively increases damage and poisons enemies.
- (Added in Repentance) Causes the ring to explode upon contact with walls or obstacles. The explosions can damage the player, causing the ring to appear again, damage the player, and cause a loop of damage.
Proptosis: The ring is much larger and deals 1.5x damage.
- (Added in Afterbirth †) The ring deals normal damage.
- (Added in Repentance) The ring is now normal size.

Holy Mantle: Getting hit when the Holy Mantle shield is active prevents Athame from triggering its effect.
A Lump of Coal: The ring damage is halved.
- (Added in Afterbirth †) The ring deals normal damage.