Until end of turn, all creatures become black and all lands become Swamps.
This effect overwrites all creatures’ colors. Creatures will be black instead of any other color or colors.
If a permanent is both a creature and a land, Nightcreep replaces all of its land types with Swamp, but it doesn’t affect its creature types. The creature land loses all abilities generated by its rules text and its previous land types but retains any abilities granted to it by other effects. For example, an animated Blinkmoth Nexus becomes a black creature land with the land subtype Swamp whose only abilities are flying and “: Add .”