Enter the following codes while playing the game and they will take effect immediately:

Code - Effect

autoaim_horizontal = 1 Autoaim left/right
auto_aim vertical = 1 Autoaim Up/Down
debug_console_commands = 1 Show console commands
no_camera_boundaries = 0 Camera is not stopped
player+demo_invulnerability = 1 Demi-God mode. Take damage, but not killed
show_fps = 1 Frame rate per second displayed
show_enemy_tactical = 1 See where Enemies will move and attack
show_polys = 1 Polygons Per Second Displayed