Razorverge Thicket

The fast-land condition reads backward off the curve, and that inversion is the whole design. Early, while your land count is still low, this enters untapped, which keeps it reliably online through the opening turns: exactly the window an aggressive Selesnya deck is racing in. Once the board has filled out and one tapped land barely registers, it starts entering tapped. The trade is honest and self-correcting: the land is at its best when you most need the tempo and at its worst when you can most afford to lose a turn. That is what separates this cycle from the painlands it shares ancestry with, which charge life on every untapped tap regardless of how deep the game has run. Here the cost is paid in late-game smoothness rather than life total, and a fast deck has long since hit its land count by then, so the one resource this withholds (an extra untapped source past the opening turns) is the one it needs least. As a Green-White source it falls into the most aggression-forward two-color pair, where the threshold maps cleanly onto how those decks sequence: lands first, threats throughout, rarely a grind long enough for the tapped clause to bite.