Armor pen... Kog?
I have a question:
Kog'maw's W does 2x attacks. So it will probaly proc armor pen 2x as fast?
If it does, then why does nobody build armor pen Kog'maw? Wouldn't it be insanely strong?
something like:

Is it because of the on-hit build overshadowing it? you know, this one:

And what if we combine them? something along the lines of:
Or
or 
Just a question. Because with the recent, ADC build armor pen META I'm suprised when I think about it that this didn't include the META.
.
EDIT: Thanks for clarifying! :)
Since he does mostly magic damage, this build isn't so strong.