Quake is a great conversion from the PC hit, and I have the cheat for the debug menu! Go to the Load option from the main menu, but do not use a memory card. Instead go to the password screen and fill it with the Q symbols, then when it tells you that you have an incorrect password, press B to exit. Now go to the options menu, and at the top will be the debug menu! This lets you have invincibility and all the weapons and a level select.
I have found two fun things to do with invincibility: One is to go to the debug menu and choose level 7 as the starting level. Go to new game and select the difficulty. You should now be at level 7. This level has very low gravity, and if you have invincibility you can aim the rocket launcher down and fire, blasting yourself high in the air! You can do the same to walls, and eventually you can blast yourself around the level with ease!
I also know how to make enemies fight each other. Put invincibility on and find an enemy with a ranged attack (e.g. Zombies) and get them to fire at you while you are hiding behind another creature. If the creature is hit it will start attacking the enemy. NOTE: No creature will attack an ogre even if they are hit by the ogre's grenade, but an ogre will attack another creature if the ogre is hit by another creature's ranged weapon.
