This effect causes the level to end when a certain sector is entered.
Tag a sector [0,65535]
. When the player enters that sector (not just touches the floor), the level will end, and the next actual map is called. So in the case of a user level, the next actual map is E1L1.MAP (unless you've added your own maps and renamed any of them E1L9.MAP).
Note: If you want to end the level with the message "We're gonna fry your ass Nukem!", tag the sector [0,65534]
. You could change the message by editing the .CON files if you really wanted to.