Help with Mod Idea

I'm Creating a JoJo's Bizzare Adventure mod, And currently I have it so that when you right click an item, it checks a global variable to see if the specific mob is summoned, and if the mob is not summoned to spawn it, and if it is summoned, to despawn the mob. This works very well in single player, but is there a way for me to implement another way to be able to be used in multiplayer; Currently, only one person can "have" the entity. In short, is there a way to be able to right click an item, then have a mob spawn, then right click it again, and to have it despawn, and for it to be used by multiple people.