User blog comment:Zilla4444/AP Version of Black Cleaver/@comment-26050883-20150128021327

Think of your standard mid lane AP champion, someone like Leblanc, Fizz, Orianna, or Akali. How do their combos work? They land 1 important skill (LB's Q, Fizz's ult, Orianna's ult, Akali's Q) and then burst you in 2 or 3 hits. If it takes 2 hits to fully stack this item and the third spell is the one that actually receives the full magic pen then what is the point of this item? You amplify your upfront burst damage a grand total of none with the MR pen and champions that have sustained damage output like Kayle would be completely broken with this item because it would give them so much more power than what they already have. Think of the champions that do well with Black Cleaver. They aren't ADCs or burst assassins, they're tanky top laners like Renekton, Darius, Garen, etc. They do well because they shred the armor of lots of targets for their team rather than for themselves. They don't do a lot of late game damage, especially not against tanks, instead the utility of the item amplifies their own damage a small amount and their main damage dealer, their ADC, a lot over the course of a team fight. The difference in design between physical and magic damage in league makes percent shredding items essentially bad for AP champions but good for AD bruisers because their ADCs deal damage over time instead of in burst so even if an AP bruiser like Rumble built this item, their own AP carries would not benefit as strongly as an ADC would from a Black Cleaver.