User blog comment:ZPPHR/Nate/@comment-70.61.75.234-20121129215436/@comment-5638912-20121129222657

This is just a concept idea, and it's not my intent to make Riot create this into the game. Of course the only source of penetration he can benefit from at the moment are the Marks of Destruction and Quintessence of Destruction, which grant both armor and magic penetration.

Anyway, I made this champion so he could only focus on building one stat (AP or AD) and switch states to make the other stat useful at some times.

Perhaps in the future we'll see items that grant both types of penetration, made for champions like this one. :P