[{quoted}](name=Akatsuki Deidara,realm=EUW,application-id=3ErqAdtq,discussion-id=rsiELqcF,comment-id=00040000,timestamp=2016-06-21T02:45:28.958+0000)
They could buff Void or other ap items. Also Void is good against tanks.
I was speaking in generalities, and generally speaking, your APC isn't going to break a tank.
One of the problems with buffing Void staff is that it acts on total MR rather than bonus. Which still makes it useful against everyone. You could do the same thing and tailor it against tanks, but likely it would leave it in a weaker state.
Also, You really need DPS to deal with the tank. Even if you could shed their MR, they have too much HP. The only HP shred item for AP is Liandry's, and that really only synergizes with DoT, and Machine gun mages. And those are really all that would actually be effective at shredding tanks.