From The TimeSplitters Wiki

We do not promote or encourage the use of Cheats when playing online. Cheats listed here are game cheats, and not action "Action Replay" or "Gameshark" etc

TimeSplitters 1 Cheats

• Paintball
• Gun Sounds
• Enemy Rockets
• All Heads Detachable
• Infinite Ammo
• Headless
• Big Heads
• Big Hands
• Small Heads
• Enemies turn to Ducks
• Enemies turn to Robofish
• Enemies turn to Bricks
• Enemies turn to Impersonators
• Enemies turn to Gingerbread
• Enemies turn to Bunnies

TimeSplitters 2 Cheats

• Big Heads
• Small Heads
• Silly Hats
• Paintball
• Fat Characters
• Slow Deaths
• All Characters Cloaked
• Cardboard Characters
• Rotating Heads
• Unlimited Ammo

TimeSplitters: Future Perfect Cheats

• 8-bit Characters
• All Characters Cloaked
• Big Hands
• Cardboard Characters
• Cascade
• Fat Characters
• Human Gun Sounds
• Old Film
• Paintball
• Rotating Heads
• Slow Motion Deaths
• Small Heads
• Spinning Heads