not enough time to waste on going through a specific build, but definitely the Frost tree, and then pair up with a Frost mage for 2v2. The synergy with those two classes will be disgustingly powerful
It's amazing in DPS and in utility, the ability to become undead is priceless, extra shadow damageis awesome and Heart Strike is a different version of MS. (combine that with saving the healing-corrupting skill and their healer will never have a moment's rest.)
Also, once you pop dancing rune blade in the right moment it's game over for any non paladin.