Admiral Pit
Smash Hero
PM doesn't count lol
Hmm..The Frozen Seaway is probably my favorite theme in MH4U, which is kind of fitting since the Zamtrios is one of my favorite monsters in the game as well. I do wish we could've gotten more monsters that used that theme though, it would've been perfect for something like the Barioth if it came back.
As for the Deviljho, there is nothing more satisfying then finally getting a quest where you can just wail on it for all those quests it ruined. I still haven't faced the Khezu, mostly because I already experienced enough horror with its cousin back in MH3U.
So tell me about the evil Khezu's cousin of the sort. All you need to know about this one is paralysis, paralysis, and more paralysis, coupled with electric attacks that can cause Thunderblight. That and the Red Khezu together in a quest caused me my first legit quest fail (unless you count me abandoning the first Yian Garuga encounter one). It ain't fun when you main Dual Blades like me.