Overload Captain in the beginning. Two Overload Minotaurs in the boss room, though the second one sometimes doesn't spawn if you defeat the boss quickly enough.
Shocker – When defeated, Goblins spawn Arc pools that cause damage over time.
Cyclops in the big room. One Wyvern in the boss room. The third Overload champion sometimes doesn't spawn in the boss room if you defeat the boss quickly enough. Boss is a Hydra that slowly teleports around.