I feel for you, I myself was cruising my no-casualties game up until the battle with Haas.
Attached are screenshots of my battle with Haas. As mentioned by the other posters, I believe the key here is to bring some bad-ass melee unit that Haas would consider debilitating with Sheep or Pygmy. In my setup, Haas simply kept on casting Sheep on my Demons, and I just kept on casting Dispel (3 guesses who won that mana battle
).
It is important to note that you should dispel the debilitating effect though; else, Haas would do something else, like Hypnotize or a damage spell. So try to bring level 4 units for him to cast Sheep/Pygmy on so that he would spend more mana. This is key.
It should be noted that I was even being pig-headed in my game, refusing to swap out the Inquisitors for something more suitable for the final battle. As such, I think I spent 40 of the 66 turns bringing them back up with Resurrection. It took me that many turns because all the enemies were zoning in on them and wiping them out completely, and I couldn't leave them at zero count since some enemy might get killed on top of them, preventing me from casting Resurrect on them. So as all the others have suggested, drop the archers for this battle. Even the Inquisitors could be dropped as you could use rage drain/chargers/resurrect to bring back lost troops.
Of course, there are two more ways to go...
spell/rage damagers + ...
1) ancient vampires/dark commander/invisibility lvl 1 + chargers + rage drain
2) demoness/anga's ruby/invisibility lvl 1 + chargers + rage drain
Option #2 necessitates you to kill the giants first and do a couple of timebacks/resurrects on the demonesses, but the results are the same.
I refrain from using these two options though since it takes the challenge out of the battles, and I actually appreciated the Haas battle a lot since I was getting a bit bored with battles before that.
