They're the card's age, condition, artwork, and availability
If these ever go below $5-6 then I think you buy in, but I would sell them at the pre-sale hype
Genetic Apex Shining Revelry Eevee Grove Genetic Apex : Most cards don't see play anymore, but the set holds a special place for nostalgic players due to the focus on Gen 1, and it does still come with some very powerful, desirable cards
As they stand now, you'll be surprised to know that this isn't even the most valuable Hyper Rare Energy card from the set
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Its tough to block a creature that can suddenly have an uncertain number of additional +1/+1 counters