Mox Poison

The original Moxen paid for their acceleration in nothing but the opportunity cost of a card slot: free mana, no strings, which is precisely why so many of them sit on restricted and banned lists wherever the stakes are real. This one keeps the free-mana half of the deal and staples on the single currency the game usually charges for that kind of power: two poison counters, landing on you, every tap. Untap, tap, poison, repeat. Five activations and you have quietly conceded the game to yourself. The design is a self-imposed clock bolted to a ramp engine, and the tension is entirely internal: the harder you lean on the mana, the faster the countdown runs out. It rewrites the classic Mox arithmetic by pricing acceleration in life-you-cannot-afford rather than cards-you-do-not-have, and the any-color fixing (the same flexibility a Mox Diamond or Chromatic Lantern would hand you) only sharpens the trap by making the thing tempting enough to actually run. There is no escaping the bill by donating the artifact away, either: the poison falls on whoever activates it, so the clock always points back at the player greedy enough to want the mana. It is a punchline resting on genuinely sound logic: take the most famous free spell in the game and make "free" mean something.