The M Gengar EX (121 / 119) card can be found in the Phantom Forces set.
Recently sold 4 times and based on those sales is worth around £12.30.
Currently, there are 7 open listings for this card on ebay.
This card sells in the range of £5.51 to £19.09, making it quite stable.
This Rare Secret card was illustrated by 5ban Graphics.
The fact that it is a EX card makes it one of the more valuable cards.