Talk:Magic Penetration/@comment-217.87.153.250-20100928085558/@comment-24.251.116.34-20101128163414

I beefed up Magic Pen on a game, it looks like the denominator is 100 plus the absolute value of magic resistance, which means that even with -100 magic resistance, you'd get -100/(100+100) and the enemy would have -50% damage reduction. There's no way to deal double damage or higher from magic pen.

Late game though, magic pen might prove useful since tanks stack up on resistance. This way your high AP character would be viable late-game.