Sonic Adventure 2
Sonic Adventure 2 was released in 2001 for the Sega Dreamcast and less than a year later for the Nintendo Gamecube as Sonic Adventure 2: Battle. SA2 was the game that introduced us to Shadow the Hedgehog and Rouge the Bat. It also allowed you to choose either the side or the good guys (Sonic, Tails, and Knuckles) or the bad guys (Shadow, Eggman, and Rouge). You had to complete both the Hero and Dark stories to unlock the final story which had all 6 characters working together to defeat the Biolizard. The Gamecube version featured a larger multiplayer mode which allowed you to also play as Metal Sonic, Tikal, and Chaos in the verses modes.