The BBF is a passive item in The Binding of Isaac: Rebirth (TBOIR)
When you pick BBF up, you get a Familiar that flies around the room and explode if it touches an enemy, dealing massive damage to anyone caught in the blast.
BBF respawns after like 10 seconds
Character has a big gray fly with a heart on its forehead roaming the room. This fly explodes if it touches a monster