This magic you seek is as complex as it is wild. It needs a reagent that can provide a stable source of continual energy, and I know of just the thing. When Archimonde met his well-deserved end here, many of his lesser minions were also killed. His chief lieutenant, Azgalor, was slain--by mortals like you, no less! You'll find the last physical remains of Azgalor in the middle of the ruins here. No need to bring all of that ash back to Ketharas. Just a pinch should be more than enough for his needs.