Urza's Filter

A flat cost reduction that discriminates by what a spell actually is on the stack, not by what it can do or what it costs. The comes off any spell that is cast with two or more colors, which is a stranger filter than it first looks: it does not care about a card's overall color identity, only about the colors it actually carries when cast. A red creature with a green activated ability is monocolored on the stack and gets nothing; a gold removal spell and a gold dragon get the same break regardless of power level. That distinction rules out a whole class of decks that look like they should benefit. Domain and converge cards, the obvious "I play five colors" payoffs, are overwhelmingly monocolored on the stack (Tribal Flames is a red spell, however many lands feed it), so building around them does nothing to turn this artifact on. The reward is only as wide as your literal gold count, and it stacks across a turn, so chaining several multicolored spells is where the flat sticker price amortizes into real tempo. The conditionality reflects an early-era project in color-pie philosophy: rather than a generic rock anyone can run, this is a payoff calibrated to making fragile multicolor manabases feel rewarded instead of punished. The artifact only spins for the kind of deck that committed to gold cards on purpose.