Any silencer, depending on my team
Psion is by far the worst since he fills so quickly. Famine/Plague need far longer to fill and what’s the issue with the horsemen is usually their third trait, which can in most cases be neutralized with a stun. Khorvash does extremely well against all horsemen, but Psion just seems pretty much unbeatable when it comes to filling up.
Spirit Fox and Wisp are just annoying.
Also depending on my team, any silencer can wreck me. I hate fighting Baba Yaga, she seems to fill up very fast and my normal team is a dragon team with TDS in third spot as the only damager.
And of course, anything that devours me is deeply hated by me since the chance to devour my troops seems to be a constant 100%. Kraken is what I see the most, but Maw+Mercy combo is definitely something I also hate fighting.
Forest Guardian is just obnoxious for me, it’s like I automatically lose if it gets to cast once. I don’t even know.
Basically, everything that deals true damage, mana-drains, devours or just drains stats automatically each round is something I hate to fight.