Creatures or critters are the indigenous wildlife in the subterranean world of Underrail. Many of them are mutated surface species adapted to living underground or BioCorp experiments, but some common animals like dogs still exist in Underrail.
Robots are the various mechanical enemies from security cameras to autonomous robotic sentries.
Humanoids are psionic apparitions, mutated humans, and other near-human creatures.
The rest are various hostile humans - bandits, raiders, gangsters and so on. See Factions for a list of all major outlaw groups.
Most critters in the wild will respawn within two hours of real time. Plants such as Mindshrooms also respawn in the same manner. Some generic human characters will also respawn. Robots and unique human characters do not respawn.
Respawning enemies will not spawn on the same zone as the player, but will the second their respawn timer has passed and the player moves to a new zone.