Invincibility:
Press Left, Square, Up, Triangle, Right, Circle, Down, X at the cheat screen.

Unlimited ammunition:
Press Down, X, Left, Circle, Down, X, Left, Circle at the cheat screen.

Slow motion mode:
Press Right, Square, Up, Triangle, Right, Square, Up, Triangle at the cheat screen.

Invisibility:
Press Left, Square, Right, Circle, Left, Square, Right, Circle at the cheat screen.

Alien mode:
Press Up, Triangle, Up, Triangle, Up, Triangle, Up, Triangle at the cheat screen.

Alternately, complete all nine Decay levels with an "A" rank. You will now be able 
to access the secret tenth mission where you will play as a Vortigaunt for the first 
time. Note: The Vortigaunt only has two attacks, the E-bolt attack and the claws. 
Note: You must start a new game or else the code will not work. After you start a 
new game, you will experience the game through the eye's of a Vortigaunt (alien). 

Xen gravity:
Press Up, Triangle, Down, X, Up, Triangle, Down, X at the cheat screen.

Bonus levels:
Press Triangle, Square, Left, Right, Circle, X, Up, Down at the cheat screen. 
Choose the "Extras" at the options screen to load new levels found from other 
discs, such as the Official US PlayStation Magazine Issue 57 (June 2002) demo 
disc. 

To get a bonus level in Decay, get one A in every section. The final level will then 
become available.

Extra health:
Buy a soda from the random soda machines. If you are impatient, shoot the soda 
machine.

Defeating Gonarch:
The Long Jump module can be used for more than moving between floating 
platforms. You can get extra height when you jump into a wall or other object. 
When you first get dumped in Gonarch's lair, to your right you may see 
white "plants" coming out of the ground. You can use these as stepping stones to 
get up on the raised area in the middle. This may not easy, but if you get up there 
Gonarch will have trouble hitting you with any attacks. It is best to use weapons 
like the crossbow for this part. You can also use the long jump technique to get to 
other places you are not supposed to, and it is useful for getting past annoying 
opponents quickly.


Hint: Using the pistol:
Use the following trick to save ammo for all guns other than pistol. Most creatures 
or persons can be killed with five or less direct shots of the pistol. 

Crabs: 2 shots or 1 crowbar hit
Zombies: 4 shots
Electric Aliens: 3 shots
Trip Bomb: 1 shot
Machinegun on stand: 5 shots
Soldiers: 5 shots
Dogs: 3 shots
Spitters: 4 shots 
Hint: Using guards:
If you have a guard, get him close enough and he will take care of almost 
anything for you. The only time you ever need to fire is if the creature is close to 
the guard. 

Hint: Barney gets cut in half:
When you enter the room where the lasers are shooting out the walls, run through. 
There should be a Barney (security officer) on the floor. Watch carefully and you 
can see the laser go across and literally cut him in half. 

 
 Game Shark Codez: 
 
 Master Code (Must Be On):
 EC8783A8 1431D934
 
 Unlock Alien Mode Cheat:
 4CA573BA 1456F025
 
 Unlock Infinite Ammo Cheat:
 4CA57372 1456F025
 
 Unlock Invincibility Cheat:
 4CA5735A 1456F025
 
 Unlock Invisibility Cheat:
 4CA5738A 1456F025
 
 Unlock Slow-Motion Cheat:
 4CA573A2 1456F025
 
 Unlock Xen Gravity Cheat:
 4CA57342 1456F025