Visions of Phyrexia

The design bind here is elegant, and it plays out across two different steps of your turn rather than one. At upkeep you exile the top card and get the choice to play it; the second payoff waits until your end step, where the game checks whether you actually spent a card from exile that turn. Impulse-draw enchantments have traditionally leaned into card advantage as their whole reason for existing, but this one refuses to give it to you for free. Play the exiled card and you spend the resource and go home empty at end of turn. Sit on it and you bank a tapped Powerstone instead, which quietly ramps toward the very artifacts and colorless activations that these decks tend to want anyway. That fork is the entire engine: every turn asks whether this turn's exiled card is worth more than a mana rock, and the answer moves as the game develops.

The Powerstone's spending restriction is what stops the ramp from bleeding into an ordinary curve. The token adds colorless that can't go toward nonartifact spells, so the mana it provides is walled off from the red cards a deck built around this is presumably casting. You accumulate ceremony toward big artifacts and activated abilities, not a faster clock. The result never floods you: each cycle converts the exile into a real card or into narrow-purpose ramp, one or the other, and rewards a deck that knows exactly what it wants that colorless mana for.