Note: this requires a bit of skill so trying it several times and dying will help you improve. Turn to face the floors and in a few seconds you will see a guard walk out of the stairway. After you kill him, he will drop a force shield, a hypo spray, and a invisibility cloak. These are "special items" because using this cheat, this is the first place you'll get them in the game.
Sent in by: Caleb Huggenberger

Enabling Cheats  -  Cheating in Oni is tough. You'll be required to use a hex editor to hack your 'persist.dat' file. If you don't know 
what we're talking about, then this cheat isn't for you, and you can activate cheats by beating the game once without cheating.

Before proceeding, make a backup copy of 'persist.dat' - without it your game will not function.

Open 'persist.dat' with your favorite hex editor. It should be located in the directory where you installed Oni.

Go to hexadecimal Offset 47 - the value should either be '02' or '06'. Change this value to '07'. Save and close the file.

Fire up Oni and get ready to cheat!

Ammo and weapon cheats  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

fatloot - Gives you all kinds of ammo and health
superammo - Super Ammo Mode
roughjustice - Gatling Guns Mode
munitionfrenzy - Creates pile of all weapons

Typing in the cheat again from the Diary screen will turn that cheat off.

Break Stuff  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you to activate it:

glassworld - Makes most objects breakable

Typing in the cheat again from the Diary screen will turn that cheat off.

Change Characters  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

shapeshifter - Change Characters (with F8 key)

Typing in the cheat again from the Diary screen will turn that cheat off.

Change Damage Cheat  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

touchofdeath - Kill enemies in one shot
chenille - Daodan Power Mode (you do more damage)
fistsoflegend - Fists Of Legend Mode

Typing in the cheat again from the Diary screen will turn that cheat off.

Change Size  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

bighead - Big Head Mode
minime - Mini Mode
behemoth - Makes you giant

Typing in the cheat again from the Diary screen will turn that cheat off.

Change the Enemy  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

reservoirdogs - Last Man Standing Mode (AIs fight with each other)
killmequick - Enemies are super tough

Typing in the cheat again from the Diary screen will turn that cheat off.

Developer Mode  -  Once in the game, press F1. This will bring up the Diary screen. Type 'thedayismine' to enable developer mode.

While in developer mode, you will have access to the Command Console. Press [`] to access the console and try some of the following commands:

[F7] = Cycle through all possible weapons
[F8] = Change character
[F9] = Start recording
[F10] = Stop recording
[F11] = Playback recording

[Ctrl]-[Shift]-[G] = toggles between slow motion and normal modes
[Ctrl]-[Shift]-[S] = toggles textures on some objects
[Ctrl]-[Shift]-[B] = shows your current opponent logic

Other handy Command Console commands:

'door_ignore_locks = 1' (unlocks all doors for you)
'ai2_kill' (kills all nearby AI)
'chr_nocollision 0/1' (when set to 1, you'll be in 
'noclip' mode, allowing you to walk through walls)

God Mode  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

liveforever - God mode
canttouchthis - Can't be knocked down or knocked back

Typing in the cheat again from the Diary screen will turn that cheat off.

Regenerate  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

elderrune - Regenerate health over time

Typing in the cheat again from the Diary screen will turn that cheat off.

Show Frame Rates  -  Press [Crtl]-[Shift]-[Y] to display your frame rate on the screen.

Slow Motion and Cloak  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

carousel - Slow Motion Mode
moonshadow - Phase Cloak

Typing in the cheat again from the Diary screen will turn that cheat off.

Win/Lose Level  -  Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

winlevel - Instantly Win Level
loselevel - Instantly Lose Level

Typing in the cheat again from the Diary screen will turn that cheat off.