Admittedly, Pokmon TCG Pocket isnt the best game for creative deckbuilding at the moment due to the presence of so many meta-defining cards that seem designed to pair perfectly with specific combinations (i.e., Mewtwo ex and Gardevoir or Moltres ex and Charizard ex), alongside the fact that there are eight or so cards that basically every deck should include
They are functionally identical to black-bordered cards and differ only in appearance, not legality or gameplay
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It punishes sacrifice effects by stealing what your opponents give up, and it forces those sacrifices regularly with annihilator 2
The card and events will come to other regions, with more info to come
Typically you are playing these cards in heavier blue decks and so UU in the cost is more of a help towards devotion than it is a hindrance to casting