Roiling Regrowth

Harrow with a delay clause. The template it descends from turns one land into two basics on the battlefield at instant speed, fixing colors and netting a land drop's worth of extra mana. What changes here is that the two basics arrive tapped rather than untapped, which reshapes what the card is for: this is not a burst-mana enabler you cast in your precombat main phase and spend immediately, but a fixer and a landfall engine that pays off a turn later. The instant-speed timing is the load-bearing part of the design. Cast it at the end of an opponent's turn and the two basics untap on your next untap step, arriving fresh for a turn where you want the mana available anyway; hold it as a response to a land-destruction spell to bank the value before your land is gone. Because two lands enter the battlefield, any landfall trigger you control fires twice, and you thin two basics out of your deck in the bargain. The sacrifice is a genuine cost, not an afterthought: a card and a permanent traded to end up with a single extra body of mana, deferred by the tapped basics. What you buy is fixing and doubled landfall priced honestly, with the tapped clause standing in for the tempo Harrow got for free.