Some marketplaces offer an instant buy-back guarantee, allowing you to recoup 85%-90% of the cards market value instantly
Better yet (or worse, depending on who's asking), you could do both and more to multiple targets, all at once
Playing to the theme of Paradox Pokemon, Professor Sadas Vitality lets you keep your Ancient Pokemon powered up by bringing back Basic Energies from your discard pile and attaching them to your Pokemon
Facebook groups dedicated to buying and selling cards as a marketplace such as Pokemon Marketplace
Legendary Creature - Human Warrior Phyrexian Imskir Iron-Eater Affinity for artifacts (This spell costs less to cast for each artifact you control.) When Imskir enters, you draw X cards and you lose X life, where X is half the number of artifacts you control, rounded down
By tapping into things that people already know in what you design, you can create cards that really tap into something people attach to