Gold Stars, which are some of Pokemon's rarest and most sought after cards, come from various sets in the EX era, which spanned from 2003 to 2007.
The Espeon (along with Umbreon) is particularly rare because it's not pulled from a mainline set, but rather a promotional POP Series 5 pack, which only contains 2 cards.
Here's what makes it special: both cards are non-holo, which means they're completely unweighable & Sealed packs now cost ~$2,000, so finding a raw copy in the wild is nearly impossible.