You can either sell it through an auction house, Pokmon card dealer, or keep it safe in a display case to preserve its value
When its defeated, exile it, then cast it transformed.) When this Siege enters, search your library and/or graveyard for a non-Human creature card with mana value X or less and put it onto the battlefield
At the store: 1 pc You can buy goods with this availability directly in our store without creating an order in advance
(Bulbapedia Mega Evolution set page)
His 1/3 body for 2 is fine enough to help stall a bit, but his ability to open up off color kicker or fix splashes is really big, and its done without having to give up advancing your board or losing mana on transition
Instead, it lets you search your library for a land card of the specified land type, reveal it, put it into your hand, then shuffle your library