Imagine seeing Ulamog, the Ceaseless Hunger having his text swapped with a Mulldrifter thats already gotten the extra value out of the enters-the-battlefield ability
This obviously implies effects we can use at instant speed, and preferably at minimal cost so we can still play normally while the dungeons tick over
Suddenly there were copies that could be bought for less than $10, and it used the exact same artwork as the original (with updated, easier-to-understand rules text to boot)
Atraxa, Praetors Voice, offers a creature that is incredibly difficult to interact with in combat that offers incredible upside in the end phase as long as you build around it
A pet deck style of mine is Miracle Grow: you play cheap creatures that grow as you play spells and protect them with light disruption while they finish the game for you
The hunt for these rare cards is an adventure in itself and makes collecting even more exciting