The most important factors are edition (1st Edition, Shadowless, Unlimited), condition (mint cards command premiums), rarity (holographic, secret rare, full art), age (vintage Base Set cards are highly sought after), and the Pokemon itself (Charizard, Pikachu, and fan favorites are worth more)
Chart shows the price of Seel [1st Edition] #41 at the end of each month going back as long as we have tracked the item.
At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.) Illustrated by Goran Josic Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Legal Brawl Not Legal Legacy Legal Comp
Blade of the Bloodchief Blade of the Bloodchief might not be as striking as some other cards, but its cheap and it likes vampires
So I decided since I was making a salty Poison deck anyway, this was the perfect opportunity to further troll the table by running Dralnu at the helm