Just level up to level 10, then spike him. You can't waste any potions on the first quest (and you can't on this if you want to win the third. Use EM and mid-fight level ups for extra mana. Honestly, if you haven't beaten the game, unlocked all gods, and unlocked all items/preps this will be rather difficult. The triple quests were designed as late game content.
We made an expansion and it is awesome. Really, you should check it out, especially if you're looking for some extra challenge.
Download over at ddmod.weebly.com!