Rhystic Circle

Spend one mana to set up a damage-prevention shield from a single source, and watch your opponent spend one mana to pop it: that is the whole transaction, and it is a fight white starts down a tempo. The "may pay" tax that defined this cycle works by forcing opponents to either feed you resources or hand you the effect, but the leverage only exists when the payoff is something they cannot afford to let through. Here the payoff is a Circle-of-Protection-style preventer narrowed to a single nominated source rather than the full swing, which means the auction settles on the smallest possible stakes. You ante up first, your opponent answers with the same mana, and at parity they keep their attacker's damage. Every activation is a miniature bidding war that the card's owner is structurally positioned to lose, since the thing being purchased was never worth much to begin with. Compare the keyword's flagship payoffs, where the tax sat in front of a tutor or a card-draw engine and the opponent's "pay or let it through" choice was genuinely painful. Attached to a marginal prevention effect, the same elegant tax mechanism produces a marginal card: a clean demonstration of how the soft-lock auction only sings when both branches of the choice hurt, and a footnote in the refinement of "may pay" design that later turned into real engines.