in the classic NES game, in some dungeon rooms, the door shut behind you, and would not open unless all the enemies were defeated. How is that done?
Shutter doors.....
Simply make a room with enemies in it. Place regular shutter doors in the room and it will work (that is, if your dungeon template screen 83 is set right and the dmap is a dungeon).
so it just "works" without anything tagged, or anything special?
The default way is to kill all enemies I believe. You can use a screen flag to make it so that you have to push a block to open it though. Just be sure to put a push flag on a block.