Challenge mode rewards:
     Complete  story  mode  to  unlock  challenge  mode.  You will get
different rewards when you complete different challenges.
     When you complete one challenge you also unlock the next one.

Challenge:                          Unlock (in Arcade mode): 
1-A Behead the Undead               Bot set: The Living Dead 
1-B Putrid Punchout                 Playable characters: Green Zombie,
                                    Brown Zombie 
1-C Dusk Of The Dead                Playable characters: Police Zombie,
                                    Skull Zombie, Jacket Zombie 
2-A Flock Around The Dock           Bot: Duckman Drake 
2-B Pro Am Duck Shoot               Cheat: All enemies are Ducks 
2-C Crispy Duck                     Playable character: Duckman Drake 
3-A Tin Man                         Bot: Robofish 
3-B Lobster Run                     Cheat: All enemies Are Robofish 
3-C Bowl Them Over                  Playable character: Robofish 
4-A Shame If Something Got Broken   
4-B Don't Wait Around               Cheat: All enemies are Bricks 
4-C Brick Flung High                Weapon: The Brick 
5-A First Impressions               Bot: The Impersonator 
5-B Lasting Impressions             Cheat: All enemies are Impersonators 
5-C Who's he Trying to Impress?     Playable character: The Impersonator 
6-A Barrel Blast    
6-B Bodyguard                       Playable character: Gasmask SWAT 
6-C Heist                           Bot & playable character: Veiled SWAT
7-A Shop 'Til You Drop              Bot: Ginger
7-B Sorry, Was That Your Bag?       Cheat: all enemies Are Gingerbreads 
7-C Everyone Must Go!               Playable character: Gingerbead 
8-A Girls 'n' Boys                  Bot: Fun-Bunny 
8-B Dinner Dates                    Cheat: All enemies sre Bunnies 
8-C Bone Grab                       Playable character: Farrah Fun-Bunny
9-A I Can't Hear Anyone Screaming   Bot set & bots: TimeSplitters
9-B Flight Delay                    Playable character: TimeSplitter 
9-C                                 Playable character: TimeSplitter