Manx TT SuperBike
At the Main screen hold X,Y, Z, L and R at the same time. You will hear a voice saying "go!" to confirm this worked. Now select a bike. Whoo.
At the "Select Transmission" screen, press Up, Up, Down, Down, Left, Right, Z, Y. Now go ride a sheep. Baa, Baa.
At the Arcade Transmission Select screen, press L, L, R, R, Left, Right, Left, Z, Y, Z. Let the time run out. Now start and check out the neat rider...
Thanks to Revolution readers Wendell E. Morse Jr. and Harvey Wallbanger!