With how much set-up is required to make this deck work, you want to look for Pokemon that can either take a decent deal of punishment or shut down the enemy, giving you the time to evolve Gardevoir or attach Energy to Mewtwo
That impacts the price, historically, as the only folks who want this card want to build around it, instead of adding it to others
There was also a new Mirran sword, the Sword of Forge and Frontier, which offered some great card advantage and ramping opportunities
But since it isnt legal for sanctioned play, Im going to move on
Not to mention you get a free attack with the copy which helps put pressure on your opponents
Second, the trample went from an activated ability to a static ability