Llanowar Behemoth

The activation cost is the whole pitch: a body that converts a stalled, flooded board into a single oversized swing. Each point of growth spends one of your creatures' taps, so the temptation is to dump the whole battlefield into one alpha strike and leave nothing back to block. Because the pump only lasts until end of turn, you pay that price fresh every combat, which is the restriction doing the balancing work. Read it as a green mana-sink that costs no mana: it turns the idle part of your board into reach on a finisher, drawing from creatures that can be tapped (vigilant blockers sitting in reserve, dorks that have not yet been tapped this turn, anything not already committed). Note the constraint the cost spells out: it taps an untapped creature, so a dork that already produced its mana this turn is spent and cannot feed it. The 4/4 frame is the floor; the ceiling scales with how wide you've gone, which is exactly the situation a creature deck wants a payoff for. It belongs to the early green tradition of build-around bodies that asked the deck to go wide before the card could go tall, and it carries the design instinct that green's late-game closers should be bought with creatures rather than with cards or mana.