Multiplayer cheat
For a new multiplayer option in Quake2, you must beat the game in the easy mode in single player. This will enable two new options in the multiplayer mode.

Bronze Cheats
To achieve the Bronze Cheats, you must end the game in the easy difficulty This will open two options for multiplayer mode: Weapons Stay and One hit kill

NOTE: Remember to save the cheats on your memory card

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.

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

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.

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.