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.
The page also mentions a handful of extra tidbits exclusive to the 3DS portable version of Sonic Generations:
All New Content
With new and exclusive environments for the Nintendo 3DS, including an un-lockable ‘special stage’. Each includes two tracks - one for Classic Sonic and one for Modern Sonic - designed to showcase each Sonics’ unique features.2 Player Versus mode
Take on your friends and earn valuable status points.Street Pass
Collect new content and unlock bonus material, increasing variety, interaction and re-playability.