When you finish comboing off you'll have as much mana as you need, a bunch of enchantments on the board, and probably not many cards left in your library
It's peaceful, and sweet, and represents Shaymin so well as the gratitude Pokemon
Out of the three this has the greatest potential for upgrades, so if youre choosing a deck to keep and build up over time, this is an excellent choice
The Dragon Energy Type returned in Evolving Skies, where star cards for the Type include Duraludon VMAX and Arceus & Dialga & Palkia Tag Team acting as the best choices if you choose Dragon
Some play into the villainous choice side of the deck, with others highlighting an overarching artifact/Dalek theme
Big RPG's have a habit of making neat little "bar games" just for their worlds, and we love it