The hostile Creeper comes in three forms - the weaker, lower-leveled Specimen b01 "Proto-Creeper", more simply known as the Proto-Creeper, the stronger Specimen b03 "Advanced Creeper", aka the Adv. Creeper, and the Archetype Creeper. Though these units share the same name as the player versions that can be promoted, the hostile Creepers are more susceptible to fire damage and are much weaker than the Rank 1 player counterparts.
These units represent the most basic of The Infected, having only one melee attack with a lengthy cooldown. They serve more as a meat shield and buffer for the more dangerous Infected units so they are more often located alone in the first row.