I did it the other day on normal with my Paladin, level 16 or 17 i think. Snake rings are good for getting your init up as is obviously the Frog princess.
Didn't have too many troubles, used inqs, blue snakes, and bears as tanks.
Just make sure you keep enough troops, rage and mana for the last battle! The quest says you have to activate the 3 different altars, what it doesn't say is once you,ve done that, you still have one more gard army to beat!
