Full pause Screen:
After pausing the game, press X + Y.
Slow Motion Mode:
While playing as Max, hold R and press Up, Up, Up, Up.
Kurt Wearing Boxers:
At the main menu, hold L + R and press X, X, Y, X.
Indy 500 Camera View:
Pause the game, then hold L + R and press B, A, B, A.
Play track two and higher of the game disc in an audio CD player to hear music from the game.
Hidden Images and Music:
Place the game disc in a PC compatible CD-ROM drive to find .JPG images and .WAV sounds from the game in the "mdk2" directory.
Boxer Mode 2667672500000001
Thanks to Revolution reader john!