Completing each Challenge unlocks the next one. In addition, beating these Challenges unlocks the corresponding game features:

Challenge 1-A: Unlock 'The Living Dead' as an Arcade Mode Bot Set.

Challenge 1-B: Unlock Green and Brown Zombies as Arcade Mode Playable Characters.

Challenge 1-C: Unlock Police, Skull and Jacket Zombies as Arcade Mode Playable Characters.

Challenge 2-A: Unlock Duckman Drake as an Arcade Mode Bot.

Challenge 2-B: Unlock the All Enemies are Ducks cheat.

Challenge 2-C: Unlock Duckman Drake as an Arcade Mode Playable Character.

Challenge 3-A: Unlock Robofish as an Arcade Mode Bot.

Challenge 3-B: Unlock the All Enemies are Fish cheat.

Challenge 3-C: Unlock Robofish as an Arcade Mode Playable Character.

Challenge 4-B: Unlock Enemy Bricks cheat.

Challenge 4-C: Unlock Brick as an Arcade Mode Weapon.

Challenge 5-A: Unlock the Impersonator as an Arcade Mode Bot.

Challenge 5-B: Unlock the All Enemies are Impersonators cheat.

Challenge 5-C: Unlock the Impersonator as an Arcade Mode Playable Character.

Challenge 6-B: Unlock Gasmask SWAT as an Arcade Mode Playable Character.

Challenge 6-C: Unlock Veiled SWAT as an Arcade Mode Playable Character.

Challenge 7-A: Unlock Ginger as an Arcade Mode Bot.

Challenge 7-B: Unlock the All Enemies are Gingerbreads cheat.

Challenge 7-C: Unlock Gingerbread as an Arcade Mode Playable Character.

Challenge 8-A: Unlock Fun-Bunny as an Arcade Mode Bot.

Challenge 8-B: Unlock the All Enemies are Bunnies cheat.

Challenge 8-C: Unlock Farrah Fun-Bunny as an Arcade Mode Playable Character.

Challenge 9-A: Unlock TimeSplitters as an Arcade Mode Bot Set.

Challenge 9-B: Unlock Timesplitter as an Arcade Mode Playable Character.