Nimbus Maze

The trick is the dependency loop: the white source needs an Island in play, the blue source needs a Plains, and neither of those lands produces the color the maze most wants to fill. That circularity is the whole balancing act. Drop it on an empty board and it taps for nothing but colorless, so the land only comes online once you already control a Plains or an Island to unlock its mirrored half. Crucially, it reads land types, not basics: any permanent with the Plains type (an original dual, a shockland, a Hallowed Fountain) flips on the blue mode, and anything with the Island type flips on the white. That makes it a payoff for manabases already saturated with the relevant types rather than a standalone fixer, which is the opposite of how most duals behave; a typical dual wants to be the only land you need, while this one assumes you have committed to Plains and Islands by other means and pays out accordingly. The colorless option keeps it from being a dead draw in the worst case, but it is a consolation, not the point. As Azorius fixing it asks a different question than its neighbors do: not "what colors do you need" but "what land types have you already got." That conditional shape, two colored modes each gated behind the opposing land type, makes it one of the more thoughtful entries in the long line of allied-color duals.