Press ~ and type "mlpdev" to enable cheat mode. Then, enter one of the following codes at the console window:
Level skip: next
Level select: map [map name]
Add indicated number of lives: addlives [number]
Restore health: health
Toggle enemy spawning: enemyspawn
Toggle master key: opensesame
Ending sequence: map end
Restart current level: restart
Display current level name: name
Show available levels in directory: dir
Show help for basic cheats: help
God mode: Shift + G
Invisibility: Shift + V
Enemy AI: Shift + B
Switch tagged enemy: Shift + ]
Self-destruct: Shift + K
Switch game information: Tab