This blue Jubjub lives in the Goldsand Shore area of the island. Forn's favourite toy is a Rainbow Balloon, but he lost it on the Rockriver Pass.
I lost my Rainbow Balloon when I was in Rockriver Pass! Would you please bring it back to me if you find it?
Great! You're super nice!
Hooray! Thanks for finding my balloon. Here's something for your trouble.
On the main site in item descriptions, he is referred to as Form. It is unclear which is his real name.