Guts

Guts is a monster that attaches itself to a wall or obstacle, such as a rock, rolling around the contour of the terrain. If the obstacle it is attached to is destroyed, then it will continue rolling in the direction it was previously traveling until it meets another wall or obstacle.

They make up for their limited movement by being very fast, and in numbers they can tighten movement space (especially in layouts containing narrow passages). Two of them are spawned by Mama Guts upon death.

Scarred Guts
Scarred Guts are paler versions of the regular Guts. They have a chance of replacing normal Guts in the. They behave identically to regular Guts but leave behind a trail of damaging Red Creep and move slightly faster than their regular counterparts.

Slog
Slogs are dark-themed versions of Guts added in The Binding of Isaac: Repentance. They still roll around, however when Isaac is in their line of sight, they charge at him.

While Guts and Scarred Guts rotate counter-clockwise, Slogs rotate clockwise.

Cyst
Cysts are rotten versions of Guts added in The Binding of Isaac: Repentance. They behave like normal Guts but they will occasionally shoot 1 blood shot towards Isaac if he is close enough.

Two of them will be spawned if a Dead Meat is killed.