More Than Meets the Eye
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At the beginning of each end step, bolster 1.
When Optimus Prime dies, return it to the battlefield converted under its owner's control.
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Living Metal
(As long as it's your turn, the Vehicle is also a creature.)
Trample
Whenever you attack, bolster 2. The chosen creature gains trample until end of turn. When that creature deals combat damage to a player this turn, convert Optimus Prime.