Marrow

Marrow is an unlockable passive item added in The Binding of Isaac: Afterbirth †.

Effects

 * Grants one Bone Heart.
 * Spawns three Red Heart pickups.
 * Grants a chance to spawn a Polished Bone upon the Bone Heart being depleted.

Trivia

 * Marrow was added in Booster Pack, after the initial release of the DLC.
 * Marrow and Smelter are currently the only items you can unlock from defeating Mom's Heart or It Lives on Hard Mode.