If were talking mounts, I've always wanted to ride an transparent ghost horse. Theres also the option of a big black cat with a witch hat or a pumpkin man to ride.
The pumpkin man would be pretty unique though to be honest, that is if you make it so the mount is holding you with the pumpkin man's vines as a way to ride it.

Althought I think that idea would be smooth, people would get candy in a boring way. Both would be neat but they'd have to implement a way for them to spawn fairly like a slower spawn rate for the lazy players and a higher for the ones fighting for the sugar.

That reminds me of the old quest in deadwood with the ghosts, and how you got hats at the end. How about something like that in the woods for halloween, and I mean make a new forest entirely for that.