Talk to them, because if they like this diablo style of play, you might scare them off. But maybe you can put the elite template on a few enemies to make it harder.

Otherwise see what the enemies have or if there are enemies with cool features. Swallow is always fun, drained is super annoying. Find enemies that pick on the weaknesses of your group. Low will? Get a scare aura on your enemies and drop the fleeing condition on the front fighter.