Talk:Devastating Strikes (Season 2014 Mastery)/@comment-20360012-20140201110202

According to http://cloth5.com/season-4-offensive-masteries-part-2/,

"Devastating Strikes yields 2/4/6% armor and magic penetration. Since % penetration as a stat is only obtainable through two items: Void Staff and Last Whisper and those items come with other stats, we only have a rough value on the % penetration stats.

Assuming Last Whisper and Void Staff are only gold efficient and not underpriced for the stats they give, then you get 150 gold worth of % armor penetration and 132 gold worth of % magic penetration.

Even if you only used one of those stats, that would be quite good. Moreover, since armor/magic penetration scales multiplicatively, taking this mastery will get you to 38% armor/magic penetration depending on which % penetration item you buy.

Lastly, let’s be honest here. Since % penetration is one of the hardest stats to acquire and is in limited supply, you want every bit you can get."

you may also refer to http://leagueoflegends.wikia.com/wiki/Offense_Mastery_Tree for details.