I really don’t mind the idea of an Oktoberfest theme. There is a ton you could do with a broad theme like that. I also like the Greek mythology theme idea that many have suggested.
But what I’d really like is a cryptids themed pin, Sasquatch, Mothman, Yeti, Chupacabra, Loch Ness Monster, Slender Man, dogmen, etc. Plenty of ways you could go with that. Could make it dark and scary or lighthearted and humorous. Animations and toy possibilities would be endless.