Faceless

The Faceless is a monster added in The Binding of Isaac: Repentance. It takes on the appearance of a Gaper with most of its head cut off. Initially, it wanders around the room aimlessly, occasionally firing out 6 blood shots in a hexagonal shape. Once it takes damage or if Isaac gets close to it, it starts to chase him and fires shots much more frequently. Upon death, it may turn into a Pacer or Gusher but more often the latter.

Fanatic
The Fanatic is a variant of Faceless, encountered only at the start of the fight with The Heretic.

At the beginning a group of 5 Exorcists are seen on the edges of a large purple pentagram on the floor, chanting and kneeling towards the center as The Heretic emerges. They are shielded until after The Heretic is fully summoned, after which they transform into Fanatics (which appear to be Exorcists with the skull replaced by a purple flame) and begin to chase Isaac, shooting two purple, rotating tears as it does so, like a Ragling.

Upon death, they have a chance to turn into Pacers or Gushers.