Shadow the Hedgehog is a 2005 platform game developed by Sega Studios USA (the former United States division of Sonic Team) and published by Sega as part of the Sonic the Hedgehog series. The game follows Shadow the Hedgehog, who suffers from amnesia, as he attempts to learn about his past while dealing with an alien invasion of Earth. Shadow the Hedgehog reintroduces third-person shooter elements from Sonic Adventure and Sonic Adventure 2, but greatly expands upon the concept and introduces nonlinear gameplay to the Sonic franchise. To defeat enemies and progress through the game, Shadow can use a variety of weapons from each faction and complete missions that will determine the game's plot and subsequently playable levels.