"The Legend". Problems with the walkthrough.

And did you beat him using only "Healing" and "Stone Skin"?

Yes, easily. I took red dragons into my army, cast Stone Skin and Healing on them, ogres helped, and the rest served as cannon fodder. Haas is very afraid of knights; he spent all his mana trying to banish them. Most of the work was done by the Reaper with his black hole, I used Gismo a couple of times, and once I protected myself with Glutton's armor. It was all over in 10 rounds.