It is truly a devastating Monarch card.
As far as strategy goes it is pretty straight forward I would use Rock Tumble when I had 2 energy cards and Crushing Mantle when I have 3 energy cards on Groudon ex and when I need to knock out a powerful Pokemon fast then I would discard those energy cards from my hand
Decklist The decklist contains one planeswalker, 24 creatures, 12 sorceries, nine instants, ten artifacts, nine enchantments, and 34 lands
Usually, sideboards need to reserve some space for Artifact, and Enchantment removal effects, but Boseiju allows such effects to be run in the main deck
No, you want this for decks that win if you give a key creature haste
He's super-auto-must-have