Blood Oath

Stabs Isaac at the beginning of each floor, draining his red hearts. Increases damage and speed for the floor based on the amount drained.

Quote

"Bleed me dry"

Effects

• Spawns a familiar that stabs Isaac at the beginning of each floor, if Isaac has more than half of a red heart. This will drain as many red hearts as possible without killing him. (leaving half a heart red heart if Isaac only had red hearts, or none at all if Isaac had soul/black/bone heart).
• Even though the animation is only a single stab when the effect triggers, it is treated as taking damage one time per half heart lost. This can lead to great synergies with items that procs on damage taken.
• For the rest of the floor, Isaac gains +(0.15 * HeartsLost ^ 2) damage and +(0.1 * HeartsLost) speed, where HeartsLost is the total hearts of damage taken from Blood Oath (half a heart counts as 0.5).
• • This amounts to a max of +19.8 damage and +1.15 speed if starting the floor with 12 filled hearts (of which only 11.5 are drained).

Synergies

• BFFS! - Adds 2 full hearts' worth of bonuses if any health is drained at all, e.g. losing 1 heart gives the bonuses of 3 hearts.

Found in

• Curse Room
• Devil Room
• Devil Room (Greed Mode)