Void Mirror

Colorless has always been the loophole in the game's cost structure: alternative casting costs paid with life or exile, free-spell pitches, mana from Eldrazi rocks and artifact ramp, all of it routing around the colored pips that spells are supposed to require. This shuts the loophole. The trigger fires whenever any spell is cast without a single colored mana in the payment, and it goes on the stack above that spell to counter it before it can resolve. That is a wider net than it first reads, because it taxes the method, not the card type. It catches Force of Negation pitched for free, an Eldrazi cast off colorless ramp, a Living End that rode in on nothing but a cascade trigger. Most hatebears name an archetype and hope the opponent is playing it; this names a behavior, and the behavior is exactly the one that lets busted colorless engines sidestep the color wheel. The elegance is in what escapes it: spend even one colored pip and you pass through untouched, so your own artifacts and colorless spells stay safe as long as you fund them off a colored source. Void Mirror only earns its slot in a deck that touches color on nearly everything it casts, which is most of them. It is a tax on the idea that mana should ever be free of the wheel it was built on, aimed squarely at the fastest, most color-agnostic corners of eternal play.