In the game's menu, go to Extras and then Cheats.

Left - Right - Up - Down - Unlimited Enchanced Vision
Right - Left - Left - Up - Down - Right - Unlimited Gas Mines
Right - Up - Right - Up - Left - Down - Unlimited Ground Pound
Down - Down - Up - Left - Unlimited Invulnerability
Left - Left - Up - Right - Unlimited Laser Eyes
Left - Down - Down - Down - Unlimited Stealth Camo
Right - Left -Left - Up - Down - Up - Unlimited SuperBark
Right - Up - Left - Right - Up - Right - Unlock All Game Levels
Right - Up - Right - Right - Unlock All Mini Games