I have no idea what the yo-yos do, but we totally need them!
A couple thoughts:
* A potion that makes a giant yo-yo drop from the sky. It acts like a reverse rainbow potion. You can jump on top of the yo-yo OR grab onto it.
* A toy that you can play with AND that will announce friends that are nearby (maybe in the same region or just a street or two away).
* A toy that you can play with that will switch your place with someone else who is playing with their Yo-Yo. Say I am in Unnu Slight and you are in East Spice... now you are in Unnu Slight and I am in East Spice.