Blossom Dryad

The whole engine here is a single tap ability that turns one land into two mana per turn cycle, the same trick Kiora's Follower and the older Argothian Elder traded on without the green creature's usual ramp framing. Untapping a land you have already used means the target worth pointing at is one that produces more than a single mana, or does something other than make mana at all: a creature-land you want to attack and mana with, a Gaea's Cradle, a Cabal Coffers, an ability land that wants to fire twice. On a 2/2 body whose only text is that tap, the dryad is less a ramp spell than a multiplier waiting for the right denominator; the value lives entirely in what it points at rather than what it is. Its quiet payoff is the loop. Pair it with a land that untaps it back, or a way to give it haste and a land worth retapping, and the once-per-turn constraint dissolves into something repeatable. That places it in the combo-piece bin rather than the curve-filler one: a green creature that does nothing at all in a vacuum and threatens to do a great deal the moment the surrounding lands justify the activation.