Optimus Prime, Hero

More Than Meets the Eye {2}{u}{r}{w} (You
may cast this card converted 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 it to the
battlefield converted under its owner's
control.