A whole bunch of developmental sketches for enemy types
Wretch : Zombie, fodder enemy
Headhunter : Stealthy attacker, easy to moderate, lightly armored by very quick. These shadowy beasts can descend on the unsuspecting from above as well.
Berserker : Bloodthirsty warrior, as they grow more powerful they encase themselves in more and more armor, by their most powerful phase they are walking tanks of death. Moderate to very difficult enemy.
1/24 edit: Cleaned up some of the text in the image