Ahhhhh! You did mention that one of the monsters had no specific way to kill it -- that they're all unique. I thought that was a cool idea at the time, but wasn't sure how the characters were supposed to figure it out. Giving them an NPC quest is a good idea.
And to clarify, I do like the lore a lot. I wasn't kidding when I said that I'd love to run this; if I get the chance, I will! :)