User blog comment:Xerav/My Random AD-Caster Item Idea etc/@comment-5254342-20121108000448

I don't know if you've seen this, but Riot has announced one of the reworked items for Season 3, the Black Cleaver, and it seems to fit your idea, with the exception of the unique active.

The Black Cleaver
 * +45 Attack Damage
 * +10% Cooldown Reduction
 * +10 Armor Penetration
 * Passive: Dealing physical damage to an enemy reduces their Armor by 5% for 6 seconds. This effect stacks up to 5 times on the same target.