The Bonus disc is to conclude "GameStop has announced the latest details on the Mario Kart: Double Dash!! bonus disc. According to the online the disc will contain the following content:
5 mini games from Mario Party 5
Playable F-Zero GX demo
Fire Emblem content that includes unlockable weapons, abilities and new music
Teenage Mutant Ninja Turtles playable demo featuring Leonardo
Star Wars Rebel Strike III Hoth level playable demo
Sonic Heroes playable demo featuring 2 levels and 3 characters and 7 all new movies" ,
pretty awesome, ive been thinking about getting GX and TMNT