Originally Posted by ModeOmega
So, if I have 400ap and I proc lichbane I get 300ap + 50ap which gives me a net loss of 50ap. But the price was reduced because the MR was removed. Take out the 400g from nullmagic and you have the same lichbane with crappier stats. Also with the change to AP damage it makes enemy stacking MR easier. Soooo....
Is this incorrect?
Why are you complaining that your lich bane benefits from your magic penetration?
Let's use your example on a tank, Volibear. At level 18, Volibear has 96 armor and 83 MR getting the defensive masteries and armor yellows with scaling MR blues, pretty standard. This drops the 400 physical damage to 204 damage. Now, you probably have 8% penetration from the mastery, and the 9 Mpen red runes, so his effective MR is now (83*.92)-9=67 MR. This drops the magic damage down to 210 damage. This is without actually building any penetration items, no sorc boots, no haunting guise, no void staff, NOTHING. Unless they have high MR, low armor, and you have no additional pen, you're doing more damage.
Also keep in mind that each MR item now provides a maximum of 50 MR each(except abyssal, don't know if that's changed), versus randuin's/FH which give 70+ Armor.