Sonic Unleashed (Wii)
Also known as: Sonic World Adventure (JP)
5 parts Werehog, 1 part Sonic, what do you get? Sonic Unwiished!
Many tutorials/missions feature strange stuff out of bounds that hint at earlier layouts.
Trial Version Leftovers
These graphics can be found in one_wii/title in the directories labeled TGS, and exist in both Japanese and English.
Unused 1-up Item Box
In Apotos' 2nd nighttime tutorial, an unused 1-up item box is loaded outside of the mission barriers, where a regular secret item box normally exists. The graphic is taken from Sonic 06 instead of the image of Sonic's head used in the final game.
Its presence in a level hints that the game used to feature a more traditional lives system (in the final game, extra lives are permanently obtained in Gaia Temples). However, collecting it does nothing now.