Can you detect with a even if a player has left or entered a game within a localscript that's placed in all player guis so they all contain it?
You can use .PlayerAdded
or .PlayerRemoved
to accomplish this. Here is a bit of code that can help get you started. Use this as a script in Workspace.
game.Players.PlayerAdded:connect(function(plr) --effect the 'plr' which is the player that just joined end) game.Players.PlayerRemoved:connect(function(plr) --effect the 'plr' which is the player that just left end)