Im creating and adventure mode map and I want a mob to spawn when a player comes within a certain area of my map. I know how to do this repeatedly but I want it to only happen once, so if the player tries going back and forth in the area after one has already been summoned, it wont work anymore. I don't want it to activate by stepping on a pressure plate. I have spent hours trying to find a solution with no luck. Please help if you can.
Why not adding a scoreboard to summon the mob only once based on the scoreboard existence o value different from zero? This way it would work even in multiplayer, you have to check the distance as well as the scoreboard.