Sonic Rush

Sonic Rush is a 2D platform video game similar to earlier games in the series as well as later ones like Sonic Advance. Levels in the game are side-scrolling and displayed using both of the DS's screens. However, boss battles, the main characters' sprites, and a special stage are rendered in 3D, creating a 2.5D effect.The game's storyline follows the intertwining adventures of a new character, Blaze the Cat, and the series' main character, Sonic the Hedgehog. (wikipedia.org)