Press L during game play to hear your character's taunt. You can
only do this while on game board, but not in mini-games. Press L +
C-stick Up for a faster version. Press L + C-stick Down for a
slower version. Press L + C-stick Left or C-stick Right to vary its volume.
Win all five boards in story mode and collect all presents for one
character. Bowser will challenge you on his board. Beat him and
his mini-game. You can now choose Bowser's Gnarly Party in Party
Mode by highlighting Koopa and pressing Right.
Besides Fruits of Doom, Darts of Doom, and Panels of Doom, there
is also a Bowser Wrestling mini-game. Go to the Bowser's Gnarly
Party Board, use a Mega Mushroom, then make an attempt to walk by
Bowser (not Bowser Spaces). You will not find him on the board in
any one except Bowser's Gnarly Party. The only other way to play
this mini-game is to go to mini-game mode (after you have unlocked
Bowser Wrestling), and look under "Etc.".
Successfully complete the game in single player mode with any
character to unlock the Goomba Stomp, Beach Volleyball, and Panel
Panic mini-games in the Extra Room.