Magneto, the Revolutionary

Other Mutant creatures you control get +2/+2
.
Power Up (Whenever this creature deals combat
damage to a player, if it does not have a +1/+1
counter on it, put a +1/+1 counter on it.)
Remove a +1/+1 counter from Magneto: Gain
control of target artifact. It becomes a 4/4 artifact creature." (You can target your own artifact.)