Blanket of Night

If this effect is applied to a snow land, the land is now a snow Swamp and not just a regular Swamp.

The land can now be tapped for black mana in addition to any other abilities it already has. This works just as if the text “{T}: Add {B}” was added to each mana-producing land. In other words, the land can be tapped for its own ability _or_ it can be tapped for black mana. Not both.

It can affect lands which do not produce mana.