Blood Oath is a familiar in The Binding of Isaac, added in the Repentance DLC.

Spawns a familiar that follows Isaac and stabs him at the beginning of the each floor if he has more than half a red heart.

The familiar will drain as much red hearts as possible without killing Isaac, ultimately leaving him at half a red heart, or no red hearts at all if he has other types of hearts that will keep him alive.

When stabbed, Isaac gains increased stats for the rest of the floor: +0.15 × HeartsLost ^ 2 worth of damage, and +0.1 × HeartsLost worth of speed.

Even though a single stab animation, every bit of damage taken is treated separately per half a heart lost, which can lead to synergies with some items.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this item for the previous Repentance version, check this page instead.

Blood Oath can be found in the following item pools:

The following tags are applied to this item:

The following special synergies and interactions for Blood Oath have been documented.

* Note that not all possible synergies and interactions are listed here.

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

Blood Oath

• Stabs Isaac at the start of each floor, depleting as many red hearts as it can without killing him
• The stab grants bonus damage and speed for the rest of the floor
• The more health sacrificed to this effect, the more stats it will provide
• Abyss: x1 locust .75x Isaac's damage

• Check out the item description on the external Isaac Wiki.