Sanguine Bond

Sanguine Bond is an unlockable passive item added in The Binding of Isaac: Repentance.

Effects

Spawns a special set of spikes in the Devil Room. They deal 1 full heart of damage per use.
Taking damage from the spikes has a chance to grant a reward.

The spikes will appear in the current Devil Room upon picking up Sanguine Bond.
The spikes will deal damage to enemies that walk or fly over them, including Krampus.
- As Krampus often spawns in the center of the room, it will deal a significant amount of damage to him, almost killing him completely.
The item causes all other spikes in the Devil Room to retract.

Goat Head: Allows Isaac to enter and leave the Devil Room at will, making this item substantially more powerful, as red hearts can be collected throughout the floor.
- Goat Head + Scapular: The spikes generated by Sanguine Bond can be farmed infinitely.
  - Quitting and reloading the game will also reset the soul heart regeneration provided by Scapular, thus negating the need for Goat Head.
Keeper / Tainted Keeper / Strawman: The pennies that are spawned when stepping on the spikes can be used to heal Keeper and infinitely farm rewards.
Placenta: With a lot of time, the spikes can be farmed infinitely.
Portable Slot: The pennies that are spawned can be gambled to give hearts, allowing more uses.
The Wafer / Percs: Hearts will last twice as long, allowing more uses. Further uses may be obtained by sacrificing the black hearts given, and any hearts added from devil room items.

This item is a reference to the card of the same name from Magic: the Gathering card game.
The item description is a likely nod to the item description of Goat Head.