Ed, if you want more intelligent/formidable/aggressive enemies, obtain and activate the following: Mythic Skull, Tilt Skull, Tough Luck Skull, and Thunderstorm Skull.

That'll double their HP, boost their resistance, guarantee saving throws, and increase all enemies' rank if possible.

Incidentally, activating the Catch Skull and the Cowbell Skull at the same time makes for lots and lots of fun.