To start with all of the extra mountains, boards, and the hidden character, enter the following code at the "start" screen (where you can select start, lesson, or option): Joystick Down, Joystick Up, D-pad Down, D-pad Up, C-Down, C-Up, L, R, Z, D-pad Left, C-right, Joystick Up, B, D-pad Right, C-Left, and then press Start. If you do this right, you'll hear a kid saying "Yeah!"
Special Moves
Jam Jam the Great: Hold A Press Left, Right, Left, Right, Hold Right Release A
Jam Jam the Wonderful: Hold A Press Up, Down, Up, Down, Hold Down Release A
Jam Jam the Fantastic: Hold A Press Down, Up, Left Hold Left, Release A
Linda Linda Spin: Hold A Press Left, Right, Hold Right, Release A
Linda Linda Poor Gourge: Hold A, Press Up, Down, Up, Down, Left, Hold Left, Release A
Tommy Tommy Spin: Hold A, Press, Right, Left, Right, Hold Right, Release A
Tommy Tommy Shaking Hold A, Left, Right, Left, Right, Hold Right, Release A
Shinobin MOVE 1 Hold A, Right, Left, Right, Hold Right, Release A
Shinobin MOVE 2 Hold A, Right, Rotate Anolog StickX2, Right, Release A
Shinobin MOVE 3 Hold A, Up, Rotate Anolog StickX2, Up, Release A
Shinobin MOVE 4 Hold A, Left, Up, Right, Down, Hold Down, Release A