Lounge

Black or green from one source is the toll, and this land pays it the standard way: it comes in tapped. The interesting clause is the one that keeps working after the manabase is full. Golgari has always closed games by grinding, and a color pair that wins on attrition wants a way to spend the mana its early plays leave stranded. Late in a game, when you have drawn more lands than spells to cast, four mana and a tap manufacture a Clue, and two more plus a sacrifice cash it for a card. The rate is deliberately punishing: nobody activates this on turn five, and you should not want to. It is a flood valve, not an engine, insurance welded onto a land you were already going to play. The lineage runs through the utility duals that gave surplus mana a job (the creature-lands that suit up to attack, the karoo lands that bounce a land back for tempo), but the reward here is raw cardflow rather than a body or a swing. What it buys is the right to run an extra land without that land being dead when the game goes long, which in a grinding color pair is worth more than a zero mana value suggests.