Optimus Prime, Hero

More Than Meets the Eye {2}{u}{r}{w} (You may
cast this card transformed for {2}{u}{r}{w}.)

At the beginning of each end step, Bolster 1.
(Choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

When Optimus Prime dies, return him to the battlefield transformed under his owners control.