50% armor pen item!
So remember how black cleaver gives 30% armor pen if you stack it over time? Remember how people called it busted because that's too much?
What if I told you that you, yes you! Can have over 50% armor pen! Here's how!
Stack 
Most champions have a natural 80 armor by the time you get these items, which let you ignore a whole 50 armor! And best of all, you can get these items for barely more than a trinity force! What a steal!
Not convinced? What if I told you that not only is the lethality stat STACKABLE, not only does it increase OVER TIME, but it ALSO WORKS ON TOWERS!
Call now.
which for some reason is allowed to exist in its current state when the majority of its users are ad assassins, yet it gives plenty of health and ad, especially when combined with transcendence rune.
...even 
and 
will occasionally grab it.
an assassin or a diver...whatever I see him building lethality all the time...