The Mewtwo (12 / 113) card can be found in the Delta Species set.
Recently sold 2 times and based on those sales is worth around £26.66.
Currently, there are 2 open listings for this card on ebay.
This card sells in the range of £23.27 to £30.05, making it stable.
This Rare Holo card was illustrated by Ryo Ueda.