SEGA's popped up an official product description for anniversary project Sonic Generations - hinting at additional characters.
On the official product page for Generations, there are the details we've seen before - classic levels from 20 years of Sonic the Hedgehog, modern and retro Sonic plus familiar bosses.
One of the more interesting highlights seem to be the ability to play alongside Sonic's captured friends and "take on more challenges with them at your side" after each level. It's uncertain who they are, whether they'd be playable or simply mirroring Sonic's moves - like Tails did in Sonic the Hedgehog 2.
The demo of the console version was recently hacked, revealing a potential list of candidates and even the presence of elemental shields, last found in Sonic the Hedgehog 3/Knuckles.