The Mewtwo (12 / 113) card can be found in the Delta Species set.
Recently sold 8 times and based on those sales is worth around £36.84.
Currently, there are 17 open listings for this card on ebay.
This card sells in the range of £27.08 to £46.60, making it quite stable.
This Rare Holo card was illustrated by Ryo Ueda.