It's amazing when a secret gets found so far down the road. F-Zero GX was released for GameCube back in 2003, and it even sported connectivity with the arcade version, F-Zero AX. Players could access exclusive tracks by inserting their memory cards into the cabinet, which is great, except for the fact that spotting F-Zero AX in the wild was a rarity.
Well, it turns out the full version of AX is actually on the GX GameCube disc. Hackers found the game hidden away, and it's fully playable with the assistance of an Action Replay or Gameshark.
If you're sitting on a copy of GX, you can find the codes you'll need here.