How would you do this? A power that can only be used under certain circumstances, but can happen at any time. Such as a power that makes you move after a successful REF save, a penalty to an opponent if they are bit by you. Yes, this is inspired by 4e, but that is the one and only thing that I really liked.
"I contend we are both atheists, I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours." -Stephen F Roberts