Bony

Revenant
Revenants are darker Bonies that guard the Mausoleum. They wander around like normal Bonies, but if Isaac gets within a Revenant's line of sight, it breathe a stream of purple fire at him for a few seconds. While breathing fire, Revenants are stationary, but will rotate to follow Isaac's movements.

Revenants are much more dangerous than normal Bonies, as they can attack from any angle. Fortunately, Revenants take a few seconds between attacks, during which time they are vulnerable.