Trinisphere

Most cost-taxers raise the price of one thing: noncreature spells, the first spell each turn, spells that target you. This one sets a floor under the entire game. As long as it stays untapped, every spell that would cost less than three mana to cast instead costs three, which is a quiet but brutal redefinition of what a turn-one play is worth. It does not care whether the spell is a counter, a discard, a fast mana rock, or a one-mana combo piece; it forces all of them up to the same tax bracket. That makes it a canonical answer to a familiar problem: decks that win before the third turn by chaining cheap rituals, free interaction, and a single explosive payoff. By making nothing cost less than three, it turns those zero-and-one-mana enablers into full-price spells, and the rituals that powered them stop generating a profit. The symmetry is real but lopsided in practice, because the fair deck running this rarely depends on a dense curve of one-drops the way the broken decks do. As stax-style tax goes, few pieces lock down a fast format this hard, and that is exactly why it lives where the most powerful and least restricted spells are legal; in any environment slow enough to play fair, the floor it sets is just an inconvenience rather than a lock.