Blanket of Night — ruling 1

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

Blanket of Night — ruling 2

Whether the land is a basic land or not is unchanged by this effect.

Blanket of Night — ruling 3

More than one Blanket of Night has no meaningful additional effect.

Blanket of Night — ruling 4

Anything which counts the number of Swamps on the battlefield will not double count an actual Swamp card while Blanket of Night is on the battlefield.

Blanket of Night — ruling 5

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.

Blanket of Night — ruling 6

The lands do not get the name “Swamp” in addition to their current name. This is a reversal of older rulings.

Blanket of Night — ruling 7

The ability is a land type change effect so it is ordered along with other land type change effects in the order they entered the battlefield.

Blanket of Night — ruling 8

It can affect lands which do not produce mana.

Blanket of Night : règles, fonctionnement et interactions (MTG)

Blanket of Night is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Each land is a Swamp in addition to its other land types.

How it works : Blanket of Night

Original English text — Wizards of the Coast / Scryfall

#1October 15, 2006· Wizards of the Coast
If this effect is applied to a snow land, the land is now a snow Swamp and not just a regular Swamp.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
Whether the land is a basic land or not is unchanged by this effect.
No other card is named in this ruling.
#3October 4, 2004· Wizards of the Coast
More than one Blanket of Night has no meaningful additional effect.
No other card is named in this ruling.
#4October 4, 2004· Wizards of the Coast
Anything which counts the number of Swamps on the battlefield will not double count an actual Swamp card while Blanket of Night is on the battlefield.
No other card is named in this ruling.
#5October 4, 2004· Wizards of the Coast
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 “: Add ” 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.
No other card is named in this ruling.
#6October 4, 2004· Wizards of the Coast
The lands do not get the name “Swamp” in addition to their current name. This is a reversal of older rulings.
No other card is named in this ruling.
#7October 4, 2004· Wizards of the Coast
The ability is a land type change effect so it is ordered along with other land type change effects in the order they entered the battlefield.
No other card is named in this ruling.
#8October 4, 2004· Wizards of the Coast
It can affect lands which do not produce mana.
No other card is named in this ruling.