Wellspring

An odd hybrid of mana fixing and theft, built on a mechanic that has almost never come back since. Most repeatable land-control effects of this era stole something you wanted kept away from an opponent for good; this one borrows a land and hands it back at end of turn, then takes it again every upkeep. The practical read is a recurring temporary loan: you produce the land's mana while you control it, and the owner regains the land at end of turn, untapping it normally during their own untap step. The upkeep untap is where the design gets interesting, and it cuts two ways. Aimed at an opponent's land, you take a freshly available land each of your turns, and because that trigger resolves in your upkeep, you have it through your main phase to generate usable mana. Aimed at your own land, the trigger still does real work: tap the land for mana in response to the upkeep trigger, let the trigger resolve and untap it, and squeeze an extra mana out of it before your turn proper. The "until end of turn" leash is what keeps the borrow honest: no permanent theft, no way to lock a key dual out of an opponent's hands forever, just a turn-by-turn loan that subsidizes your development without ever denying theirs. That narrowness is also why the effect stayed buried. Wizards has circled temporary land control through other shapes since, but this upkeep-triggered borrow-and-return loop remained a Mirage curiosity: a green-white experiment in turning enchant-land into a clock-based mana subsidy rather than a clean tempo weapon.