Phyrexian Vindicator, a creature with a similar damage-blocking ability is moving up in price too, because it plays very nicely alongside everything that works well with Anti-Venom
Another technique is to sort them by generation, such as first generation, second generation, and so on
Pauls involvement with the card game has also drastically increased the rarity and pricing of certain cards
A cards condition also significantly impacts its value, whether holo or non-holo
M Skarmory only has one attack that allows us to target any Pokmon on the field and deal 220 damage
But then again, Toons are currently very low tier in the meta, so I think them benefiting with this idea does not make them broken