User blog comment:Zilla4444/AP Version of Black Cleaver/@comment-5015210-20120611205727/@comment-4070227-20120612153656

I think the main idea behind this was, Black Cleaver was designed for AD champions that auto attack as their main sorce of damage (sometimes enhanced by their spells) and wanna get rid of some of their opponents armor.

Then there are the casters who cast spells as their main sorce of damage. And there version of BC is malady... which they have to get four auto attacks in 8 seconds then use their spell to capitalize on the magic reduction. Which is unpractical because they will take a lot of harrasment from the other spell caster while they are just sitting in their auto attack range taking harrasment making it not worth it.

While this item helps with that problem. As you do not have to sit there doing no damage autoattacking, and taking more damage your self. But with this item you can use your spells more effectively, being able to reduce their magic resist the same amount as malady but without that punishment that just makes it not worth it.