I don't know much about Pokémon cards, but I know this is a rare holo. Is it worth much?
Backstory: my son (6yo) kept talking lately about a Mewtwo he got at a birthday party and how he's going to trade it with his classmate for a Darkrai, but he lost his Mewtwo somewhere in the car. So yesterday I finally get around to searching below the car seat to find this. A holo Mewtwo Vstar, in a protective sleeve too. I asked him repeatedly if it was really in the goodie bag (making sure the b-day kid didn't just give it away on their own without parents knowing), but yeah, everyone got cards in their bags (but doesn't sound like anyone got something like this one). For now I told him to just keep it safe and not use it to play with and definitely don't trade it away.
Also, be aware that a cards "value" is often inflated. At the end of the day, the card is worth what someone will give you for it.