Minamo, School at Water's Edge

Five lands in this cycle shared one chassis: tap for a color, then spend that color plus a tap to do something flavored around legends. This one untaps a legendary permanent, and the word "permanent" rather than "creature" is where the trouble lives. The flavor reads as a school whose waters keep the mythic dragons and divinities flowing, but the absence of a type restriction means any legendary land, artifact, or enchantment that taps for value can be reset for a single blue. Point it at a legendary source that produces more than one mana and, so long as you can cover Minamo's own tap, you come out ahead: the untap costs the same blue regardless of how much you free up, so the payoff scales with whatever else you have in play while the printed text gives no hint of a ceiling. The other four lands in the cycle attach a real opportunity cost to their second ability; this one's cost stays flat while its output is dictated entirely by what it gets pointed at. That open-endedness is the reason a card that looks like blue fixing with a cute rider keeps ending up on the watch lists of eternal formats. It stands as a clean lesson in templating: "untap target legendary permanent" with no creature clause hands a land an engine its designers almost certainly did not price.