So having other variants of him like Fearless Fighter and Neverland Hero will allow you to get this card onto the field early
I would try to get Umbreon into the game early on so you can start confusing your opponent's Pokemon, but if you can't get it out early, I would recommend putting it on your bench, attaching three energy cards to it, and waiting for your opponent to put a Pokemon with a lot of energy cards attached to it in the active Pokemon spot, I would then move Umbreon into that active Pokemon spot and use Shadow Shutdown until Umbreon is knocked out or retreated, I would hope to get lucky and flip 2 coins so my opponent would have to discard all their energy on that active Pokemon
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Noteworthy cards include Dialga ex, Palkia ex, and Pachirisu ex, alongside Generation 4 starters Turtwig, Piplup, and Chimchar, as confirmed by the short announcement trailer for Space-Time Smackdown