Birthday Scavenger Hunt - bring your super sleuthing skills we're going hunt down all kinds of things for [name] birthday this year! Costume contest for best dressed "detective."
Make a little booklet of "clues" where each page has an easy puzzle that provides information about the party. Looking for the information sets up the spirit of the party.
Wording for scavenger hunts is endless as far as the possibilities of what you can call it. Invitations should definately catch the eye and captivate the person invited. "Redward...Pirates Booty" works as being on the cover.