First, it has an incredibly high 330 HP, which lets it stay up even after being hit by many of the strongest moves in the meta
Darkrais Nightmare Aura ability paired with tools like Poison Barb and Rocky Helmet can counter Oricorio, and Giratinas huge burst damage potential can bring down Meowscarada
That plan may involve taking fast Prize cards with a powerful Pokmon ex, setting up a Stage 2 attacker that can take repeated knockouts, spreading damage across the opponents board, denying Energy, disrupting the opponents hand, or trading efficiently with smaller Pokmon
Lots of people goldfish their decks to test them out, and theres nothing stopping you from playing against yourself with two decks
(Note: This method applies only to top-loading or resealable inner sleeves
They serve several important purposes: Protection: Play with valuable cards without risking damage to your originals