Halloween Scavenger Hunt Riddles?

Some friends and I are having a Halloween SCAVENGER HUNT this holiday and I’m trying to come up with some relatively difficult riddles.

We’re all college aged, so I need some hard yet solvable riddles to keep everyone interest. Each clue is going to be a riddle that leads to the next clue until we reach the prize at the end. So the riddles are going to hint at different locations around the area. We’re planning to have the party at someone’s house, so the clues can be outside or inside.

Any and all suggestions are very welcome!