Enchantment 
(CMC:3)
Each mana-producing land is a swamp in addition to its normal land type.
"Kaervek imprisoned Mangara out of jealousy, but he taints Jamuraa simply out of spite."
—Asmira, Holy Avenger
VI • EN
Cliff Nielsen
™ & © 1993—1997 Wizards of the Coast
Legal in: Mirage Block,Legacy,Vintage,Freeform,Prismatic,Tribal Wars Legacy,Singleton 100,Commander
Oracle Text (click to copy):
View this MTG card on Gatherer 10/4/2004
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 "{Tap}: Add to your mana pool" 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.
10/4/2004
Whether the land is a basic land or not is unchanged by this effect.
10/4/2004
More than one Blanket of Night has no meaningful additional effect.
10/4/2004
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.
10/4/2004
It can affect lands which do not produce mana.
10/4/2004
The lands do not get the name "Swamp" in addition to their current name. This is a reversal of older rulings.
10/4/2004
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.
10/15/2006
If this effect is applied to a snow land, the land is now a snow Swamp and not just a regular Swamp.
Card Blanket of Night is not on TCGPlayer.
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