Amonkhet Raceway

A colorless mana source that untaps into far more once your speed climbs, and the climb is the whole design. Early it is just a tap for one colorless: nothing else, no payoff, a slot you pay for on the promise of later. Speed ties the unlock to the tempo of your own aggression, ratcheting up once per turn whenever an opponent loses life, capped at four and staying there once it arrives. Reach the top and the land grants haste at instant speed for the cost of a tap, which is the part worth building around: not haste as a one-turn enabler but haste feeding the same loop that powered it. The creature you deploy this turn gets to attack the turn it lands, that attack drains an opponent, and the next threat gets the same treatment. It is a self-sustaining pressure engine rather than a single burst, a subtler use of the keyword than the usual "swing the turn it enters." The gating is the balancing act: a deck slow enough to stall never crosses the life-loss threshold enough times to reach max speed in the first place, so the ability sits dormant in exactly the decks that would most want a free effect. It rewards commitment to the aggressive plan and offers nothing to the one that stumbles out of the gate.