[{quoted}](name=Sona Ping,realm=NA,application-id=3ErqAdtq,discussion-id=OFhb0hPv,comment-id=0000,timestamp=2015-07-16T23:25:36.712+0000)
This is kinda more for Tips & Tricks. Anyway...
It's worth it in that Hybrid Runes cost far less than getting both a set of Armor Pen and a set of Magic Pen and in that you give up rather little magic pen. stats for a lot of armor pen. However, of course, the Armor Pen. is only useful on your base auto attack damage.
I'm pretty sure your wrong. What you are thinking of is flat reduction.
I didn't mean reduce their armor, i used the wrong choice of words. I meant like it'll make them take more damage, as IF they were negative armor.
Does it work that way?
Like if they have 0 mr and you have 20 magic penetration. Would they take damage as if they would have -20 mr?