Short answers, pulled from the story.
Nix was discovered on the 15th of May 2005, with confirmation images taken on the 18th of May 2005. The discovery was announced publicly on the 31st of October 2005, after precovery of archival Hubble images from 2002 confirmed the finding.
Nix was independently discovered by Max Mutchler and Andrew Steffl, both members of the Pluto Companion Search Team. They used the Hubble Space Telescope to search for faint moons around Pluto.
The spelling was changed from the classical Nyx to Nix, the Coptic form of the name, to avoid confusion with the asteroid 3908 Nyx already catalogued in astronomical records. The International Astronomical Union approved the name Nix on the 21st of June 2006.
Nix has an elongated shape with measured dimensions of 49.8 by 33.2 by 31.1 km. New Horizons images taken from about 231,000 km gave an approximate measurement of 42 by 36 km, and mission scientists described its outline as resembling a jelly bean.
Nix tumbles because the gravitational pull of Pluto and Charon varies as they orbit their shared barycenter, tugging at Nix in irregular ways. Its elongated shape amplifies the effect by creating torques on the body. Between 2005 and the 2015 New Horizons flyby, Nix's rotation rate increased by 10 percent.
New Horizons images revealed a reddish area approximately 18 km across on Nix's surface. The leading explanation is that it is an impact crater where material from beneath the water ice layer was thrown onto the surface. Trace amounts of frozen methane reacting with ultraviolet radiation to form tholins is a secondary explanation for reddish material on Nix.