First and foremost, it brought the first variant Pokmon to the game: Dark Pokmon
The ability to enter the battlefield as any creature type you choose is powerful on its own
Early cards, prize cards distributed at events and contests, and cards in strong condition that have received high grades from third party authentication services are attracting attention not only for nostalgia, but also for their cultural and asset value
Most recently of all, the announcement that the Pokmon TCG will be bringing back Trainers Pokmon after the best part of three decades was a welcome surprise for many
Banlist History Restriction changes recorded for Armor Breaker
Cards with this powerful of an effect are simply not printed at this mana value any longer, and if they are, like Goryo's Vengeance, they have a built-in limitation