Gyre Sage

Most mana creatures pay a fixed dividend: tap, get one mana, every turn for the rest of the game. This one starts as a 1/2 that produces nothing and offers an accelerating return instead. Evolve does the bookkeeping: every creature you play with greater power or toughness stacks another counter, and each counter is another point of green when it finally taps. The design tension lives in how far apart the floor and the ceiling sit. Cast it into an empty board and it does nothing; cast it into a curve of progressively larger creatures and it snowballs into a mana engine that funds the same big spells that triggered it in the first place. That two-step (grow the body, then untap and dump the mana) is what separates it from a Llanowar Elves you slot in and forget. It also rewards anything that adds counters outside the evolve trigger, since the green-per-counter clause does not care how the counters arrived; a proliferate effect or a counter-doubler turns the tap ability from ramp into a payoff. Each counter does pull double duty: the same +1/+1 that swells the mana output also raises the toughness, so a well-fed Gyre Sage becomes a genuinely sticky blocker on top of an engine. But the body is the investment vehicle, not the prize. This is a creature built to be grown into, and the reward scales with how committed the rest of the deck is to going wide and tall.