User blog comment:Emptylord/Archived/PBE Patch Notes (Preseason 3)/@comment-23.30.226.209-20121128211240

Black Cleaver currently has no UNIQUE abilities on it.

The cooldown, flat armor pen and % stacking armor pen.

I haven't had a chance to see how the % armor pen stacks - does it stack up to the cap for each (allowing 60 or 90% - which seems off to me) or do more Black Cleavers just increase the rate at which it reaches the 30% cap?