Code

every 1 tick:
	loop all players:
		if slot 8 of loop-player's inventory is not nether star:
			if loop-player's inventory contains nether star named "&c&lSky&b&lBlock &e&lMenu":
				remove 1 nether star from loop-player's inventory
			set slot 8 of loop-player's inventory to nether star named "&c&lSky&b&lBlock &e&lMenu"
		if slot 8 of loop-player's inventory is nether star:
			stop