Sonic Unleashed, released as Sonic World Adventure in Japan, is a video game in the Sonic the Hedgehog series developed by Sonic Team and published by Sega for multiple platforms in 2008. The game follows Sonic the Hedgehog as he attempts to restore the world to normal after his nemesis, Doctor Eggman, splits the world into pieces, as well as his struggles with his new beast form, Sonic the Werehog. Gameplay features two distinct styles, with each being played either during daytime or night-time. Daytime stages incorporate Sonic’s traditional platforming and trademark speed, with a combination of behind-the-back third-person viewpoints and 2D side-scroller platforming; gameplay seamlessly transitions between these two views. Night-time levels see Sonic transform into the Werehog; gameplay slows down to accommodate greater platform play, and involves combat against waves of enemies using the Werehog’s brute strength.
The game’s existence was first brought to light when Sega trademarked the Unleashed name, and shortly after, images and a gameplay video were leaked to the public in March 2008. Public anticipation for the game was high, owing to the video’s demonstration of some two-dimensional gameplay, seen as a possible return to Sonic’s platforming roots. However, critical reception for the game was mixed, with reviewers praising certain elements, such as the sense of speed in daylight stages and the graphics and audio that make up the environments, and criticizing others, such as the new Werehog game mechanic, as well as several gameplay and design concepts. Reviewers felt that Unleashed was ultimately not the title that would be able to reinvigorate the series. This is the final Sonic the Hedgehog game released for the PlayStation 2.