Metapod.

During your opponent's next turn, whenever 20 or less damage is done to Metapod (after applying Weakness and Resistance), prevent that damage. (Any other effects of attacks still happen).

Flip a coin. If heads, remove all damage counters from Metapod. Then, search your deck for a card that evolves from Metapod and attach that card to Metapod. This counts as evolving Metapod. Shuffle your deck afterward.