Nyx (or possibly Nix) is the name of Roxy Lalonde's browser of choice, and is therefore presumed to be the name of the Denizen of her land. If this is the case, Nyx would likely be the Denizen associated with Void, and thus presumably also Equius Zahhak's denizen in the Land of Caves and Silence.
In Greek mythology, Nyx is the primoridal goddess of the night, and mother of Hemera. Appropriately, the icon for Nyx is identical to Hemera's flipped horizontally, with the color changed to purple. The colors of the two (orange and purple) could also be reflective of the dichotomy between Prospit and Derse.
Combining Nyx and Hemera also produces something remeniscent of Calliope's caduceus chat symbol.
The "Nix" spelling may be a reference to the colloquial term for "nothing," as Roxy is a Void player.