Ok, so I am trying to make a cosmetics plugin. Since I've been coding for a few months now and wanting to make my own server with custom plugins, I decided to. But. There was a problem whilst developing the cosmetics plugin. I know to make all of the cosmetics, GUI's etc... but when it comes to actually getting the cosmetic (winning it by opening a cosmetic box and then unlocking it forever) I realized there was a problem. I could've put the player that got the cosmetic in an arraylist which detects if you have the cosmetic or not, but I heard that .yml files act weird when they get large. Is there any better solution to this? I am not asking for code, just a theoretical soultion. Any help would do.