Cheat mode:
Press ~ to display the console prompt. Enter one of the following codes to activate the corresponding cheat function.

All weapons, unlimited ammo	impulse 9
All weapons, full ammo, all keys	impulse 11
Super shield	impulse 255
Invincibility	god
Press [Space] to fly	fly
Toggle no clipping mode	noclip
Gain # shells	give s<number>
Gain # health	give h<number>
Gain # nails	give n<number>
Gain # rockets	give r<number>
Gain # cells	give c<number>
Get weapon #	give <number>
Commit suicide	kill
Monsters will not attack unless hit	notarget
Level select	map e<episode>m<mission>
Sets difficulty level	skill <0 - 3>
Silver key	impulse 13
Gold key	impulse 14
Quadruple damage	Impulse 255
Reduce gravity by x%	sv_gravity <number>