Any plans for more or different mods?  Some general ideas:

Spiders that zig-zag

rats that stop and start some times 

Bigger mobs with health bars (take multiple hits to kill)

Different schools of magic  for both mobs and yourself 

Mobs with resistances and weaknesses to certain elements

Multiple mobs rushing at the same time making the player need to hit all their shots to not loose  hp

More attackers as the game progresses