Talk:Last Whisper/@comment-217.131.92.40-20120831121044/@comment-4499980-20120901211221

Armor reduction (like the one from the Black cleaver) reduces the target's armor, and so everyone attacking that target would benefit from the reduction.

Last whisper increases your own armor penetration. Since it's percentile armor pen, the amount of armor you actually ignore is based on how much armor your target has.
 * target has 250 armore → you ignore 100 armor.
 * target has 100 armor → you ignore 40 armor.
 * target has 60 armor → you ignore 24 armor.