Because its a Stage 2 card, its a little more difficult to set up, but it might have a place in some Psychic decks built around control
The Agony of Choice In competitive decks, adding a card is often a matter of playing the which is better? game, with the loser being removed from your deck
They possess a move that lets them potentially block all incoming damage while reflecting 20 points back to the attacker on their turn, though Mewtwo's trainer must use Reflect Shield in advance for it to take effect
A collectors dream and a competitive curveball all in one
The only thing the player needs to do after attacking is to discard the top 5 cards of their deck, which will rarely be a bad thing for players basing their strategy around this card.
Drawing cards is one of the best incentives for any strategy, and players already know that this card needs to be killed ASAP