User blog comment:Lykrast/Double the items/@comment-16494910-20140302150549/@comment-7481207-20140302213024

You shouldn't stack rabadon's because its the most expensive 120 AP item yet both the cheaper ones give other stackable stats, while only the AP from rabadon's does. There is never a reason to have more than one rabadon's, even when you're going for as much AP as possible (in which case one of the 6 items should be a Mejai's).