(later) Yes yes! Shadow is here! But ah crap, he's likely a rival boss instead of playable. I'll stick with a mod or dlc. Is that supposed to be Mephiles, a fusion of him and Time Eater, or someone else entirely?
Probably not, like in previous Sonic Generations he's merely an obstacle, a rival testing the Sonics and the OC, or a mind-controlled pawn of the final villain.