Mewtwo-EX #XY183 from XY Black Star Promos is a reverse holo promo card that currently sells for about $6.07 ungraded, with graded copies ranging from $13.48 at grade 7 to $475 at grade 10. A grade 10 copy sells for around $475, about 78× the $6.07 raw price, so high-grade copies are worth grading.