ZombieLoffe, I'll cut you some slack since you've been sick,
but trigger_once doesn't have a start 'off' property. However, your idea would work using a multisource as the master of the doorway trigger_once. Then the trigger_once in the room could target the multisource, so when you leave the room the doorway trigger would fire. As for the fade/level-change, I have an example map called
Teldelay that shows how to control a fade/teleport, which could be converted to control a fade/level-change. Dark Phoenix, your idea can be done. If you want to pull it off, it looks like you'll be learning a lot about multisource!