Tumors
Tumors are enemies that slowly float across the room, diagonally bouncing off walls.
This page is about Tumors added by Fiend Folio. More information about Tumors in general can be found in the vanilla page.
Benign
Benigns are juvenile variants of Tumors that slowly drift diagonally through the room and retaliate to damage by firing 3 evenly space projectiles with a random orientation.
Unlike Tumors, Benigns will not attack on their own.
Minimoon
Minimoons are juvenile variants of Planetoids that can be found in Utero. They float diagonally through the room rapidly, and upon getting close enough to another enemy they will orbit it for about a half rotation. The Minimoon will then fly off in a new direction at that angle, bouncing off walls. Unlike other Tumors, Minimoons do not have any attacks.
If an enemy a Minimoon is currently circling is killed, they will be immediately released from orbit.