Megatron, Destructive Force

Living metal (as long as it's your turn, this
Vehicle is also a creature.)
Whenever Megatron attacks, you may sacrifice
another artifact. When you do, Megatron deals
damage equal to the sacrificed artifact's mana
value to the 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 Megatron.