I have only fought Malistair by helping a friend so the best combo would have to be........ Keep Frost Gainting if you are Ice, or if you are fire keep Fire Dargoning, or if you are life just use anythinng and heal up, if you are Death then dont use death just use your secondary moves , if you are balance just keep Judgmenting, or if you are Myth just keep Orthurusing and if you are Storm then just keep Tritoning. And I hope this helps.
I'm a level 70 Balance wiz, who still hangs out in DS and farms Malistaire pretty often. Here's how I roll (without treasure cards):
#1: Blade, Spirit Shield, Fortify, Vengeance, Amp, Ra. If I don't have Ra in my hand at the moment, Power Nova will work just as well- either one, if done properly, will one-hit the minions.
#4: Balanceblade, Bladestorm, Spirit Shield, Fortify, Vengeance, Amp, Judge. If I critical, with a full-pip, bladed, amped Judge, this hits around 5-8k.
(insert random heals, Justice Slashes, to ward off Weakness-spamming, Unbalance, and TCs, as they are required).
My wife and I defeated him last night. We are both necromancers. We laid a prism down, then 3 different feints (normal, tc, gear) and bladed. She hit first and one shot defeated him with a secondary school Centaur. We planned on just laying down prisms and then use bladed Wraith, but it was not needed.