Polished Bone

Polished Bone is an unlockable trinket added in The Binding of Isaac: Repentance.

Effects

After clearing a room, adds a 25% chance to spawn a friendly Bony.
- 25% of spawned Bonies are Black Bonies.

Golden Trinket / Mom's Box / multiple copies: Copies and boosts increase the chance to spawn Bonies, first to 33%, 50%, then 100% at 4 copies. However, the chance becomes virtually zero with 6 or more copies due to a programming oversight.

Ace Cards: Friendly monsters are still affected by Ace Cards.
Blood Puppy: Either version of Blood Puppy will target friendly enemies and can drag them along with it when it charges them. Blood Puppy cannot damage friendly enemies; however, friendly enemies can damage Blood Puppy despite not targeting it.
Broken Modem: Broken Modem also affects friendly enemies and projectiles created by them.
Eraser: Bonies erased by Eraser will never spawn again, greatly diminishing the value of Polished Bone. If Black Bonies are also erased, Polished Bone becomes useless.
Ghost Bombs / Hungry Soul / Purgatory / Vade Retro: Explosions from ghosts can kill friendly enemies.

Bug!	Each use of Glowing Hourglass that does not move Isaac to a different room than the one he is currently in (such as the starting room of a new floor) will duplicate friendly enemies.