At the end of your Battle Phase, if this card attacked or was attacked, return this card to your Deck unless you discard 1 card.
However, the part thats causing some mixed opinions is the text in the lower right corner of the card: Mega Evolution ex rule: When your Mega Evolved Pokmon ex is Knocked Out, your opponent gets 3 points. The rule mirrors the one found on cards in the main Pokmon TCG game
Control decks like Snorlax Stall benefit from Eri, a new supporter that lets you look at your opponents hand and discard 2 item cards, disabling their switching options
You can also go with the hard ramp route by using Arbor Elf+Utopia Sprawl For dragons to capitalize on, I would recommend guys like Goldspan Dragon or Terror of the Peaks or Obsidian Charmaw or Demanding Dragon
Just as a little bonus, its ultimate ability is also pure value, giving you an emblem that turns the lands in your hand into flashback-versions of the spells in your graveyard, cause why not