Now that murdus mentioned a new mosnter class, I find myself proopeled to post this.
I would really like to see a new Class that can apply Mana Burn to enemies (hintWraithhint) as its one of the two status effects that you cannot deal to monsters (the other one being weakning).
As for what it would do, It could make Monsters with magical attack deal phisical damage when aflicted by it, and work like poison when it comes to monsters getting rid of it.