The Mewtwo GX (78 / 73) card can be found in the Shining Legends set.
Recently sold 7 times and based on those sales is worth around £51.00.
Currently, there are 6 open listings for this card on ebay.
This card sells in the range of £27.62 to £74.38, making it highly volatile.
This Rare Secret card was illustrated by Mitsuhiro Arita.
The fact that it is a GX card makes it one of the more valuable cards.