Alternate ending:
Locate every hidden piece and solve the puzzle before completing the game to view a different ending.
Achievements:
1989 - Kill 1989 enemies
60 To Car - Go to the car 60 times
Aced It - Get an A+ on any chapter
Achievement Whore - Unlock all achievements
Always On Top - Perform every ground kill in the game
Batman - Clear chapter using only a bat and the bat mask
Cat Fight - Kill the panthers using the panther mask
Combo Beginner - Perform a 4x combo
Combo Intermediate - Perform a 6x combo
Combo King - Perform a 12x combo
Combo Master - Perform a 10x combo
Combo Pro - Perform a 8x combo
Dog Lover - Kill 99 dogs
Domino Effect - Throw a weapon at an enemy so that his weapon hits another
Eye For Details - Collect all the puzzle pieces
Get A Life - Get A+ on all the chapters
Guns For Show - Kill at least one enemy with each gun
I Got New Friends - Unlock all weapons
Karma - Die 1000 times
Knife For Pros - Kill at least one enemy with each melee weapon
Let In Some Air - Destroy 500 glass panels
Nigel Lowrie - Use a human shield
Pitcher - Hit at least one enemy with each throwing weapon
Plain Luck - Kill three or more enemies with the same brick in one throw
Playing Pool - Kill an enemy with a brick bounced against a wall
Sewer Alligator - Find the crocodile mask
Smell Something Burning - Kill the crapping gangster with a fireaxe
Sounds of Animals Fighting - Wear all masks at least once
That's It? - Beat the epilogue
The Boss - Solve the puzzle
The End? - Beat the mainstory
These Are My Guns - Complete chapter five barehanded
This Is It - Beat the epilogue with secret ending
Two Birds With One Stone - Kill two enemies with the same brick in one throw
Zoo Keeper - Collect all the masks