Cheats
At the extras menu, use the D-pad to enter the following:

Paintball Mode - Right, Left, Right, Left, Down, Down, Up, Up
Unlock All Skins In Mutliplayer - Down Left, Up, Left, Right, Down, Left, Up

Unlockables
To unlock One Life Mode complete all stages on hard difficulty.

At the end of a level, you see your score and these symbols that come up at the bottom of the screen. They are called Octopi. You can have up to five Octopi. In order to get Octopi, you must get enough points from beating the level.

Auric Enterprises Art	Get 2 Octopi at Auric Enterpirses
Auric Enterprises Art 2, Multiplayer Modifier: Lethal Strike	Get 5 Octopi at Auric Enterprises
Crab Key Art	Get 2 Octopi at Crab Key
Crab Key Art 2, Multiplayer power-up: Speed Loader	Get 5 Octopi at Crab Key
Fort Knox Art 2, Multiplayer Modifier: Random Weapons	Get 5 Optopi at Fort Knox
Fort Knox Art, Goldeneye implant, and SPEC 9 side-arm	Get 2 Octopi at Fort Knox
Hong Kong Art	Get 2 Octopi at Hong Kong
Hong Kong Art, Mulitplayer Power-Up: Adrenaline	Get 5 Octopi at Hong Kong
Hoover Dam Art	Get 2 Octopi at Hoover Dam
Hoover Dam Art 2, Multiplayer Modifier: Eve Overcharge	Get 5 Octopi at Hoover Dam
Midas Casino Art	Get 2 Octopi at Midas Casino
Midas Casino Art 2, Multiplayer Power-Up: Regeneration	Get 5 Octopi at Midas Casino
Multiplayer Map: Bathhouse	Get 3 Octopi at Hong Kong
Multiplayer Map: Carver's Press	Get 3 Octopi at Auric Enterprises
Multiplayer Map: Dr. No's Reactor	Get 3 Octopi at Crab Key
Multiplayer Map: Fissure Platform	Get 3 Octopi at The Octopus
Multiplayer Map: Goldeneye's Retreat	Get 3 Octopi at Volcano Lair
Multiplayer Map: Midas Vault	Get 3 Octopi at Midas Casino
Multiplayer map: Pump Room	Get 3 Octopi at Fort Knox
Multiplayer Map: Turbine	Get 3 Octopi at Hoover Dam
Multiplayer Skin: Auric Elite	Get 4 Octopi at Fort Knox
Multiplayer Skin: Dr. No	Get 4 Octopi at Crab Key
Multiplayer Skin: Dr. No Elite	Get 4 Octopi at Auric Enterprises
Multiplayer Skin: Lair Elite	Get 4 Octopi at Volcano Lair
Multiplayer Skin: Lair Gaurd	Get 4 Octopi at The Octopus
Multiplayer Skin: Oddjob	Get 4 Octopi at Midas Casino
Multiplayer Skin: Triad Informant	Get 4 Octopi at Hong Kong
Multiplayer Skin: Xenia Onatopp	Get 4 Octopi at Hoover Dam
Octopus Art	Get 2 Octopi at The Octopus
Octopus Art 2, Multiplayer Modifier: Rapid Eye Recharge	Get 5 Octopi at The Octopus
Volcano Lair Art	Get 2 Octopi at Volcano Lair
Volcano Lair Art 2, Multiplayer Modifier: Turbo	Get 5 Octopi at Volcano Lair