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)
Importantly, because you cast that spell, youre even going to get cast triggers out of your Eldrazi
A two-drop artifact for graveyard hate when both Soul-Guide Lantern and Ghost Vacuum are already in the format at a cheaper rate
Finding one is the collector's equivalent of a perfect game
Remove three study counters from this enchantment, Sacrifice this enchantment: Draw seven cards