All Disks:

D-Disk: Beat the game. Go to the Team Snagem Hideout and Find Gonzap. Near him is the D-Disk. Use: Getting to the Deep Colloseum (You face every boss in the game again.)

L-Disk: In the Deep, you find the Golden Teeth. Go back to the Under, and give the teeth to the old man near the Under Colloseum. Use: Getting the Amulet Coin.

R-Disk: After giving the Machine part to Nett, go to the elevator you used to first get in. You'll see a sequence. Go down when you get to the area where they captured Sylvia. Go Right again, and press A. Use: Getting to Venus's Hideout.

U-Disk: After getting off the Subway, you usually would go up, but go left through the maze of boxes. Use: Getting another Time Flute.