Unlock Evil Character:
When you have completed the game in Normal mode press Up, Up, Down, Down, Left, Right, Left, Right.
When you complete the following tasks the corresponding character wil become available. These characters can be used in Survival modes and have different stats that will not carry over if they are used in Story mode.
Buy everything in survival mode.
Survive 15 consecutive waves.
Kill an enemy with a sink.
Unlock Chop Chop:
Perform 60 pistol counter kills.
Unlock Classic Shank:
Kill a goon by throwing a bomber.
Perform 100 turret kills.
Complete Campaign on hard.
Defeat all waves of a survival map.
Reach the zombie wave in each survival map.
Perform 50 fire trap kills.
Perform 100 grenade kills.
Complete Campaign on normal.
Perform 20 bat counter kills.
Purchase an item in survival.