Like most Pokmon cards, the value of Ho-Oh-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 (BREAKpoint)
Ramp early and survive until you can cast or cheat in The Ur-Dragon
This card sees play in nearly every green deck, even decks where green is just a splash color, from Galea, Kindler of Hope decks to Vorinclex, Monstrous Raider decks and Wulfgar of Icewind Dale decks
The reverse-holo is beautiful, making the art pop out even more
Iconic Elemental cards come in the form of Omnath, who has four versions to pick from, and Yarok, the Desecrated, who doubles up your enter the battlefield triggers