Poison mist requires you to bring a healer at least (I bring 2 for safety). It leaves a lot less room for error, and I have to bring some HP potions just in case.
Magic Night is annoying, but only for some heroes. The ones that cut mana like Li Xiu or those that summon minions like Buddy are safe, since those effects are not status based. Also worth noting that status effects from items (atk- from axes for e.g.) are NOT affected by the 1 turn limitation.
Dense Fog… that one sucks. If I bring anyone who hits the enemy, I try to at least make sure they have some other useful effect should they miss. For e.g. Lancelot at least buffs attack and mana generation, if he misses.
Underwater is probably the most annoying though. The 13 turn limit… can’t do anything about it. Just gotta get good boards and stack against the minions. Bring battle items for the end bosses. The underwater damage is no joke either, at least for poison mist you can stay relatively healthy with healers, drowning damage though is brutal.
So I’d say the underwater ones are probably the hardest to deal with.