Chrome Mox

Mox Diamond asks you to pitch a land; Lotus Petal sacrifices itself for one burst of mana; this took a different route to the same fast-mana problem and made the cost a permanent hole in your hand. The artifact is free to cast and free to tap, but the card you imprint is exiled for the game, and the mana it produces is locked to that card's colors. That is the entire negotiation: you accelerate by one mana on turn one in exchange for playing down a card going forward, and only down the right kind of card, since artifacts and lands cannot feed the imprint, and a hand thin on castable spells leaves the Mox an inert rock that taps for nothing. The discipline is in what imprint refuses to let you do. A free accelerant that drew from any source would warp every deck that could afford it; tethering the mana to an exiled card means the decks that want it most are the ones with cheap, redundant spells to spare, the combo and storm shells that would rather convert a fourth copy of a one-drop into speed than cast it. It descends from the zero-cost rocks the original Moxen opened, but where those simply made colored mana, this one prices the acceleration in the texture of your hand: the right spell to throw away can decide whether the rock is a launchpad or dead weight.