Loki, Asgards Destroyer

Living metal: (As long as its your turn, this
Vehicle is also a creature)
Whenever Loki attacks, you may sacrifice
another artifact. When you do Loki deals
damage equal to the sacrificed artifact's mana
value to target creature. If excess damage
would be dealt to that creature this way,
instead that damage is dealt to that creature's
controller and you convert Loki.