Talk:Miss Fortune/@comment-6000413-20140513150259/@comment-4636093-20140513174212

Black Cleaver is never worth it unless you have at least 2 other heavy sustained DPS ADs on your team.

It gives a stacking 5% armor shred debuff each hit for a total of 25% after 5 hits.

Last Whisper gives a perminant 35% armor pen.

And even if you DO have at least 2 other heavy physical DPSs on your team then it's usually better for one of those to pick it up instead. Wukong or Garen spinning can apply the debuff far more reliably than MF ulting.