Mage soloing her at lvl 110, the mana drain was the worst problem. Merc was completely drained before she hit 60% health, I thought of bailing out but thought I'd see how far I could get.
As it turned out, her DPS was not that brutal so I managed to keep my pet healed. Mana ran out at about 20% but by using a clicky-rod I kept going and she went down eventually. Close call.
Solo 110 Mage ~ Air pet EM XXVII