Like most Pokmon cards, the value of Charizard-EX depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (XY Black Star Promos)
Billy Brennan
To tie-in with Magic's 30th anniversary, there's one promo card for each of the years Magic has been around - Dominaria United had Serra Angel, Ball Lightning, and Fyndhorn Elves from 1993, '94, and '95
Enchanted creature gets +2/+2 and has vigilance
Mime (6/64) has always been a polarizing Pokemon -- you either love the design or find it unsettling -- but that distinctiveness is exactly what keeps demand steady
Until the hype dies down, and its unclear if that will happen anytime soon, Id expect Hordewing Skaab to maintain a high price tag