Gold Cheat:
     To  get  gold  you  must beat the game on hard. Winning gold will
give you infinte ammo, all weapons and all the rest of the multiplayer
codes you recieve when you win silver and bronze.

Silver Cheat:
     To  enable  Silver  Cheat,  finish the game in MEDIUM difficulty.
This  will open 2 more bars in multiplayer mode : Game Speed and Blast
Force.  Plus it will unlock the multiplayer cheats you get for winning
bronze.

Bronze Cheats:
     Beat  the  game  on  the  easy difficulty. This will give you two
options for multiplayer mode: Weapons Stay and One hit kill.

Invincibility:
     Pause game and press L2, L2, R1, R2, R1, L2.

Kill Final Boss easily:
     First  when  you enter the boss room strafe one step to the right
so  you  see  the  tank  commando  and shoot him down with your rocket
launcher  when  he's dead run forward to the flying enemy and run from
right  to  left  and  shoot at him with your hyperblaster and when you
dont  have any more ammo take the minigun and do the same thing again.
Then  you shoot the other tank commander with your rocket launcher and
when do the same thing to the flying enemy

Hidden multiplayer areas:
     In the Hydophobia level, go into that hallway thats all red. Stop
in  the center and you'll notice a darkened area on the wall. Shoot it
and  it  will  reveal a BFG10K. There's another secret. In the pool of
water  by  the super-shotgun, jump in and shoot the center of the wall
by the shotgun to reveal a quad damage.

     In  Toxic  Vats level,go into the narrow hallway with a ladder on
each  side.  Take the ladder that brings you to the platform where you
can get on the moving crane thingy. Take the hallway to the part where
you're  standing  on  the  glass platform with the hyperblaster on it.
look  down  through  the  glass  and  you'll  be able to see a railgun
submerged in a small section of the toxic waste. Jump in and swim down
and get the railgun.

Infinite ammo:
     Take the chaingun, which is weapon number 5 in the list, and then
press  the  fire  button.  Keep  holding it down, and then change your
weapon  to  anything  else. Now you should have unlimited ammo on your
chaingun  AND machine gun if you did it correctly. This may take a few
tries.

Hints:
     If  you  want to save a game whenever you want, just walk back at
the beginning of the level, there you can save.

     If  you  need more bullets for machinegun or vulcan (you know the
big rotating one) take the vulcan. Then shoot and hold it, during that
choose  another  weapon.  Now you should have unlimited ammo for those
two  guns.  The  same  you can do with the hyperblaster in multiplayer
level toxic vats (you must finish the game on medium first)

     Walk on the place where you can find the hyperblaster, then shoot
till you have 37 bullets left. Then switch to machine gun, do the same
trick as above, now you should have unlimited ammo for the best weapon
in the whole game.

     If  you  really  want  to beat your friends on multiplayer, first
enable  one  hit  kill. After that begin the game, run like mad to get
the  hyperblaster  to defend yourself for a couple of minutes. Then go
after the BZG when you have it, simply aim at the ground and jump (set
gravity  on  zero, or else you are toast), try to control and then you
have  to  shoot  but you must blast of when you are in the top of your
jump.  If you shoot then you are able to fly for about one minute. You
can  navigate  yourself while flying to look up and down, walk forward
an  backwards.  If you are very good at it, you can even make a salto.
Imagine  yourself what happens when you make a looping 360 degrees and
shoot at the same time with a hyperblaster.

     Before  you  walk into a corridor or a small section always check
the  walls.  There  are  over  a hundred secret rooms in the 1st three
levels.

     If  you walk on the 6th level (maybe 7th) then you will see a big
hole  under  you  lava  in it. You can walk over it by enable a button
which  will  make  a bridge, first you must do that. Then do something
unexpected:  Throw  yourself  into  the  lava!  You can swim in it. Be
carefull! You only have 15 seconds, before you burn out. You will find
an  BZG  weapon,  the green beam cannon blaster from multiplayer! This
weapon  is  very  handy  against  the  tanks  and  ecpecially the tank
commanders.