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Hello, there is nothing for Silent Hill 3 so I'll put this guide up for fun biggrin

Type in these Codes for new costumes beat game first before unlocking
Suspense 13eme = Rue
PutHere2FeelJoy = Block head
TOUCH_MY_HEART = Don't Touch
EGMpretaporter = EGM Shirt
gameinformer = Game Informer Tank Top
ProTip = GamePro
SH3_Wrestlarn = Gamereactor
iaml33t = GameSpy.com
GMRownzjoo = GMR shirt
IwannabeaGJ = GN
GangsterGirl = God of thunder
cockadooodledoo = Golden Rooster
HappyBirthDay = Heather Shirt
IGN_pickleboy = IGN.com Shirt
BlueRobbieWin = Killer rabbit
SH3_OPiuM = Official Playstation Magazine costume
I_Love_You = Onsen
extra_thumbs = OPS2
sLmLdGhSmKfBfH = Play
MATADOR = PS2RO
badical = PSM Tank Top
01_03_08_11_12 = Royal flush
LightToFuture = The light
PrincessHeart = Transform Key
ShogyouMujou = Transience
Shut_your_mouth = Zipper

Bold: this costume has the powers of the "Sexy Beam"

EXTREME MODES
to unlock the extreme modes, you must beat the game on Hard Action and Hard mode, there are more extreme modes, they range from 1 to X(10).
after beating X, you get the God of Thunder costume

Health Bar
Complete the game on Hard Action Mode and Hard Riddle Mode to unlock the life bar, which can be turned on and off at the extra options screen.

Unlock Weapons
TO Unlock the Following you must BEAT THE GAME ONCE!

Beam Sabre:
Kill more enemies by Combat than shooting. This weapon turns into the Sexy Beam when you have the transformation Key equipped.

Flamethrower:
Kill more enemies by shooting than combat. you will get it automatically on your second run through if you didnt get it on you first.

Gold & Silver Pipes:
these are a bit special of items to get:
Heather will ask if you'd like to throw the steel pipe in the sewers, SAY YES!
then *poof* THE SEWER FAIRY! she asks you three simple questions, the order is: NO, NO, YES.
these pipes are the same as the steel one, they are only for design purposes...

Atlernate Douglas Costume
Beat the game once, select ''Extra New Game'' option at the main menu and press Up twice, Down twice, Left, Right, Left, Right, O, X. Heather will sigh after you choose a difficulty and riddle level to confirm the code. During the scenes where you see Douglas, he will be wearing no pants at all, quite humorous razz

New Scenes
BEAT SILENT HILL 2 FOR THIS TO WORK AND HAVE IT ON THE SAME MEMORY CARD AS SILENT HILL 3!!!
New interactions with some objects and new scenes will now be available. The scenes are similar or with some type of reference to SH2. For example, Heather trying to look for something stuck into the toilet in the mall.

ALL I have for now!

I think its killing 30 monsters with the Heather Beam before getting to your apartment. Once you get to your aparment it should activate.

i don't think the Supreme 13eme is an actual code, but i could be wrong.
Here's some extra tips and cheats:

Silent Hill 2 References (They've been posted already, but these kinda go into detail):

Examine the stalls in the girls bathroom at the mall. Heather will attempt to pull something out of the toilet. She gets grossed out and stops. Then she asks if there was anyone who would do something so gross as that
Examine the brochure at Heaven's Night. I's the pamphlet James reads at the prison about a tourist guide to Silent Hill
Examine the section of fence on the Brookhaven roof (where James was hit by Pyramid Head) The fence will look like it won't break easily, although James destroyed it in the last game when he fell.

Secret Death Scenes:

In the hospital, allow yourself to get killed by the nurses. Viatel will come, prop Heather's legs open and drag her away.
Attack Clauida after she kills Vincent. Heather will birth the god. You don't see it, but you can hear it.
In the subway, jump onto the tracks and walk down a tunnel. A train will run Heather over.
Exit the rear of the train and walk off. Heather will break her neck falling off.

Cheats!!!!:

Brookhaven Hospital: 2nd Lobby Door Password----> Easy=4639; Normal=8634; Hard=4896

Bookstore Puzzle----> Easy=8964; Normal=4523; Hard=8352

Brookhaven Hospital: 3rd Lobby Door Password----> Normal=4756; Hard=1328

Brookhaven: Crematory Room Puzzle----> Normal=9367; Hard=9271

Brookhaven: Suitcase----> Easy/Normal= Stop the alarm clock and put in the numbers (i.e. 8:12 would be 0812); Hard= Stop the clock and put the time in in military time (i.e. 8:12 would be either 0812 or 2012 depending on how it goes.)

its tough gettin the posessed ending but keep workin on it