Mario Kart: Double Dash!!/Unlockables

Mushroom Cup

 * 50cc:Green Fire (kart)
 * 100cc:Rattle Buggy (kart)
 * 150cc:Luigi's Mansion (Battle stage)
 * Mirror Mode:Toadette Kart (kart)

Flower Cup

 * 50cc:Bloom Coach (kart)
 * 100cc:Waluigi Racer (kart)
 * 150cc:Turbo Birdo (kart)
 * Mirror Mode:Tilt-a-Kart (Battle stage)

Star Cup

 * 50cc:Para Wing (kart)
 * 100cc:Special Cup (Cup)
 * 150cc:Barrel Train (kart)
 * Mirror Mode:King Boo & Petey Piranha (character combo), Piranha Pipes (kart)

Special Cup

 * 50cc:Bullet Blaster (kart)
 * 100cc:Toad & Toadette (character combo), Toad Kart (kart)
 * 150cc:All Cup Tour (Cup)
 * Mirror Mode: Boo Pipes (kart)

All Cup Tour

 * 50cc:Nothing
 * 100cc:Nothing
 * 150cc:Mirror Mode (Engine Size)
 * Mirror Mode:Parade Kart (kart)

Once you win every cup, you get a new "Thanks For Playing" screen and a new title screen.