First, its a cool item, a little edgy maybe, but still a really cool idea. I have one problem with it though, a 2 minute cooldown on a passive that you don't have a choice when to activate it? a few things i would like to say
FIRST- i know why you want it like this, so someone cant pop in fight for a second get em low pop duskblade then run away while they die
SECOND - a remedy for it that does not involve an involuntary 2 minute cooldow, make it a active on the next auto attack, but can only be activated while out of combat, so you cant pop it int he middle of a fight to cheese a kill which is what your avoiding by making it not an active.
FINALLY- shouldn't this be melee only? it currently does not state it is, and i most certainly think it should be.