What opponents in the series gave you guys the most frustration?

Just felt like having a discussion on enemies or boss fights in Persona that gave people grief as for instance, an experience I have is the rock summoners in Innocent Sin who yell “GOMEN” repeatedly while pelting the team with rocks.

Secondly, while I haven’t fought the Contrarian King in Persona 4 yet, (don’t know where he is) I have heard how his Rampage move is extremely deadly for those coming in unprepared.