This could be a private message or anything you want, but I just wanted to make this I thought this was interesting.
Ok, first, of course, place down that Zone! Place down an Item Granter, granting anything you want. Then, place down a Checker(The Infamous Device), and set it so that it is checking if you have the item(Greater than 0). Now, put down the thing you want to only show up once. Wire the Zone to the Checker, and set so that ‘Player enters Zone → Run check’. If Check Fails, grant Item(Item Granter), and if Check Passes, do nothing.
There! You’re done! I hope this was helpful!
-@Blizzy