Quake 2 Codes -

Easy difficulty bonus:
Successfully complete and save the game under the easy difficulty setting to unlock the "One Hit Kill" and "Weapons Stay" options for multi-player mode.

Medium difficulty bonus:
Successfully complete and save the game under the medium difficulty setting to unlock the "Game Speed", "Blast Force", "One Hit Kill" and "Weapons Stay" options for multi-player mode

Hard difficulty bonus:
Successfully complete and save the game under the hard difficulty setting to unlock the "Unlimited Ammo", "All weapons", "Game Speed", "Blast Force", "One Hit Kill" and "Weapons Stay" options for multi-player mode

Hint: Defeating Makron:
To defeat Makron easily, just strafe around the pillars and shoot rockets at him. Be quick, since he can take you down with one shot from the BFG 10K. When the robot machine gets destroyed, stand in a corner of a pillar and angle your view so you can hit him. This will cause him to become confused and walk back and forth. Use grenades or rockets to destroy him.

Instead of using rockets and dodging the big pillars, use the underground tunnels to lure him over and kill him. If done correctly, this can be done without him getting a shot on you. Open both doors that are on opposite sides of the room by pressing the blue insignia buttons on the floor. Once you do this, run to whatever side he is on, then sit and wait until he is in plain view. Light him up with either the chain gun or the hyperblaster. You can even use the shotgun, but it may be too slow. If he is reluctant to show up in front of the door, you can step out quickly in plain sight, then back up quickly.

Hint: Defeating the level 4 Boss:
When you are towards the end of the level, you will have to fight and destroy a very large orange robot. Use the following tactics to avoid getting any damage. Stay in the hallway that you go through to fight the Boss. Get your rail gun out and open the door. You will see the Boss to your left. Aim and take two shots -- any more, and you will get hit hard. Back up and go straight down the hall. Wait for about ten seconds, run forward so that the door opens, and shoot. Retreat back and wait until the door shuts. Then, run forward as before, let the door open, shoot, and retreat. Repeat this until the Boss is defeated.