The way I did it was use Berserk,Protect,Shell & Haste on two characters & use one for healing. The berserked characters cut through the ice elementals with ease and when Mateus's health bar is 7/8 empty or so(by this time the berserk will have worn off) use a chain of quickenings of about 6-8 and he will be dead. I did it with all my characters round level 25 first time. Plus I don't recall him using sleep but I watched a friend of mine fight him and he did cast it so equip your healer character with a Ninjinshin Belt if you want to be safe rather than sorry.