Shadow gives over the fourth Chaos Emerald in this game, a possible tribute to Shadow's memetic line, "Where's that damn fourth Chaos Emerald?" from his earlier spin off title, Shadow the Hedgehog (2005).
Like the Wanted Poster bearing the cameos of several characters, there are also two Missing Posters of Mighty the Armadillo from Chaotix (1995) and Ray the Flying Squirrel from SegaSonic the Hedgehog (1993). Both posters say "Missing since 1993."
Early on in development, a third Sonic character representing the Dreamcast Era would have been in the game. Ryan Drummond the voice actor for Sonic in Sonic Adventure 2 (2001) and Sonic Heroes (2003) was invited to return for this role but Drummond refused as it would have required him to leave his union.
There were plans for ports for the Nintendo DS, PlayStation Portable and Nintendo Wii.
20th Anniversary project for Sonic the Hedgehog.