A few years back they collabed with Namco/Bandai to have Pac-Man characters in “Sonic Dash,” and a Sonic themed maze in the official Pac-Man ap.
Sonic is honestly no stranger to crossovers, he’s done many. Archie, Sabrina, IMAGE comics, Megaman, Mario, Smash Brothers, the afforementioned Pac-Man mobile crossover, Hello Kitty, Cartoon Network’s “O.K. K.O.,” and now Angry Birds.
The Ninja Turtles even cameo’d jokingly in the background of an old Sonic comic. (Back when Archie Comics Inc published both Sonic, and TMNT. Now coincidentally, IDW publishes both franchises, so a Sonic X TMNT crossover is possible.)