Tranquilizer gun Mini Game:
Beat the game once.
Beat the first 3 missions without running out of continues. This will enable missions 4, 5, and 6.
Play as Bruno from Die Hard:
Collect every illustrations in all three missions.
Play as Cindy from Die Hard:
Hold Start while selecting Ivy to play as Cindy.
Play as the Monkey:
Beat missions 4, 5, and 6 to enable the monkey.
Pause game and press A + L + B + Y
Anytime you have a handgun you can do this. Knock the enemy down, and when they are getting up stand behind them (so when they get up you would be directly behind them) and point a gun at them. Hold both triggers (L, R) and press fire. Your man/woman will yell "Freeze punk...". They will kneel on the ground, that's your cue to fire again. This time he will slap on the cuffs and the bad guy will jump twice and fall.
Thanks to Revolution readers Joe Campanella, Kamikazi playa', Topher, MotoRacer, A.J. Garttmeyer, and JElias8863!