Sega has confirmed that Sonic is the only playable character in the recently delayed Sonic the Hedgehog 4: Episode 1. While that means that there will be no random side characters that Sega likes to make, it also means that the game lacks Tails and Knuckles, two characters that have been with Sonic since the second and third games respectively. As far as later episodes, Sega hasn’t confirmed or ruled anything out.
Just Tails and Knuckles. Please.
