Quirion Ranger

The free activation cost is the whole engine: bouncing a Forest to your hand isn't a payment so much as a deferral, because you replay the land the same turn for no net mana loss. That accounting trick is what turns a one-mana 1/1 into a combo piece. Untapping a creature once per turn reads like a minor combat trick (ambush a tapped attacker, free a blocker), but the historically important application is untapping a mana creature: pair it with an Elf that taps for more than one green, such as Priest of Titania, and the Forest-bounce-replay loop becomes a repeatable mana source, converting a single tappable dork into multiple activations per turn and feeding green's fastest ramp lines. The "activate only once each turn" restriction is what keeps the whole thing honest; with a strong enough mana creature and enough Forests to keep returning, that single clause is all that holds the engine linear rather than explosive. Note that "Forest" means any land with the Forest type, so an original dual or a shock land qualifies just as readily as a basic, which quietly knits the card into the wave of landfall and land-untap effects that came later: replaying a land each turn triggers everything that cares about lands entering. A one-mana Elf that asks nothing of your mana to operate: the kind of low-rate, high-ceiling design that ages into a staple because the cost was never the rate, it was the deckbuilding it demanded.