From what happened with a trade I did this was my experience. They asked me to first trade them the pets that they were upgrading with the stone. They upgraded them traded them back and I traded the pets to them. Not sure if you can use the stone on another persons pet thou. Hope this helps.

Tons of fun Good luck everyone.

I have Muckbreath Chuck Toothy Snarly and Tiny Shale Spider. I'm interested in a combo of the critter and aquatic stones for the lot of them. id - Malanora#1166