New AP item

We need a new ap item. Y'all railed the ap assassins with this new item. We need an ap item that either negates crib like randuins, or something else the gives us a shield/armor. Ap assassins don't normally get rod/liandrys/crystal scepter so we don't have many health options. I was thinking maybe an item that gives us a temporary armor boost once we've taken a certain amount of crit dmg or after taking a certain health dmg, gain a temporary shield. Hourglass is good, but the cd on it is long as hell and we're still getting one shot by talon/zed/yas with this new lethality and armor pen. oh and the item should give ap too, maybe even some --> magic pen <--