I was able to beat the first two guys on Plague last night but the third one kind of kicked my ass. He starts with 75 HP even on Normal, what gives? I guess you're supposed to take advantage of those weird things that give you +8 to attack if you kill them?
Yep, keep control of the board and get as many units as you can out, kill a spore for +8 and take him out. You will have to do it again as a hunter in the class challenge.