I want to make a hack and I'm not sure how to set where Mario spawns. I tried entrances, if that has to do anything with it. But when I load the hack into my emulator It's just nothing and then I fall to my death. Edit: I set the "Normal" Entrance ID to 1 and then set the level config "Start Entrance" to 1. Same thing happened.

Entrances are correct, you just have to set things right.

1st: If you have an entrance, click on it. you should now see the "Entrance ID". Go to Level Config and change the "Start Entrance" to this number (most likely this is 0).

2nd: Once done, you need a so called "View". Basically, this thing tells the game where it can move the camera. You can add one by choosing the View menu in the editor and click "Add". A square called "View" + number (eg View 1) should appear. Set this so the View contains the whole level. Then go to the Entrance and enter the View's number there.
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previously (un)known as BooChewbaca

Thanks! It worked.