Ukko is one of my worst nightmares. It is the most insane enemy to me, he ended many good runs... Being killed by the Ukko is very frustrating. I also hate Shotgun Hiisi and probably Robo-Cop

I do think the Robo-Cop is the worst of them. This thing can kill you very quickly if you're in his fire range...

i did enjoy your evaluation though, and got me thinking about my own top annoying list.

#1 missile tank - tough, tracking, quick reload
#2 regular tank - tough, rapid fire
#3 Sniper - perfect aim
#4 Thunder mage - large blast radius
#5 Hiisi Leader - minions
#6 Ice Spirit - the hex pattern ice that releases freezing vapor
#7 Ghost - always finds a wand
#8 any worm - angering the gods
#9 Hiisi Alchemist - lava and acid potions
#10 Big Toad - never see it in time to dodge. a problem on first level before i find stronger wands