Consult population reports from grading services to estimate actual rarity
However, perhaps the best Tera support card is a stadium, as it allows players to set up numerous evolution lines on their bench

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And as a plus side to not having an irrelevant boost to 100 HP, you can easily search it out with a Level Ball
And I am sure everyone has their favorite (mine is Emergent Ultimatum)
In short, Pokemon League promo cards are a symbol of success for participants and winners