Item idea: Blood Sacrifice

Do you know these games where mid, bot and jungle were all doing fairly well, but then the enemy 37/0 enemy Riven top comes down and singlehandedly wins the game?

Well, here's an idea:

Name: Blood Sacrifice Stats: -Unique active (melee range): kills the user, and deals the user's current HP to the target champion as physical and magical damage, depending on the user's Armor and Magic Resist.

Using it against a non-fed enemy would simply make a 4v4 out of the 5v5, with marginal gain for your team, and its short range would give outplay potential in the form of kiting and peeling; also, its scaling on HP and resistances would make it pretty much only useful on tanks, who'd give up their survivability in order to take out that single threat.

What do you think about this?