Urza’s Saga common. Black is the only color with such a core philosophy of trying to get you to play more and more of the color to the exclusion of other colors. Often that commitment shows up in mana requirements, such as Drain Life’s cost or Frozen Shade’s ability, where more black mana means more power. But a related family of black cards rewards you for having more swamps rather than just having more black mana. (Some other examples are Nightmare, Dakmor Sorceress, Infernal Harvest, and Mutilate.)
