When you're going for this achievement, be sure to make the right choices in the final cut scene. If you side with the bad guys, you fight five paladins who are NOT the Grand Enemy. If you want to see all of the cut scenes available, I suggest saving immediately after you defeat the mini-boss (who is not mini at all, and probably harder than the true Grand Enemy). Fighting the GE, all you need is something with a reasonable enchantment, and patience. Swing, swing, jump back. Swing, swing, jump back. Keep that up, and you'll walk away without a scratch.
DON'T FORGET TO SAVE.