Talk:Haunting Guise/@comment-118.208.234.245-20110514190615/@comment-209.169.90.44-20110606041526

That's a fair waste of build items and runes. You're looking at more like ((MR - 30) - 50) * .55. Magic penetration can never reduce below 0, so anything more than necessary is wasted. The 55% penetration doesn't apply until after reduction and flat penetration, so your void staff becomes less cost efficient with all of those other items.

Take a look at this page if you don't understand where I'm talking from: http://leagueoflegends.wikia.com/wiki/Magic_Penetration