When used, spawns one of the following things for each enemy already killed in the current room:
An orbital bone familiar (very common).
A friendly Bony (uncommon).
A friendly Black Bony (rare).
Orbital bones deal contact damage equal to Isaac's damage at the time it was spawned, repel enemies that touch it, and will block 3 shots or deal 2 ticks of contact damage before being destroyed.
Bonys deal 8.3 contact damage and 5 damage with thrown bones.
Black Bonys will explode on death, dealing 40 damage to enemies it hits. The explosion will also hurt Isaac if he is in range.