Here are 6 Joypolis Japan exclusive flat keychains.
It's rather too bad the photo is so small, you can't really tell what they are made of. It's possible these have 'sketchy line' edges. You can collect Amy, Shadow, Eggman, Tails, Sonic & Knuckles. Amy appears to be...walking? Shadow is pointing, Eggman is in the Eggomatic, Tails is flying, Sonic is sitting and...doing something/unclear what, & Knuckles is sleeping while the master Emerald is behind him/but really it's so large that his keychain is mostly about the Emerald instead of him. (A bit of an odd choice)