Ok... So you're able to fully play as Sonic, Silver, and Shadow. In the very last level, you're able to play as Super Sonic, Super Shadow, and Super Silver. In select levels (mainly the one before the last one) you're able to play as Tails, Knuckles, Blaze, Amy, Rouge, and Omega.
Good bye everyone, it's been fun!
Special thanks to ED_, superman4u, and Cross Stinger
Credit for the Siggy goes to shadow slayer