SEGA was having a character countdown to show what characters would be playable in Project Needlemouse. Come day 5 only Sonic remained on the character list. So unless SEGA pulls a fast one, Sonic should be the only playable character in the title.
SEGA also released concept art for one of the enemies to appear in Project Needlemouse. You can check out the art after the jump.
(Source: Sega Blogs)