Short answers, pulled from the story.
Xiangliu was discovered by a team led by Csaba Kiss. The find was formally announced by Gábor Marton, Csaba Kiss, and Thomas Müller on the 17th of October 2016 at the 48th Meeting of the Division for Planetary Sciences.
Xiangliu was identified in Hubble Space Telescope images taken with the Wide Field Camera 3 on the 18th of September 2010. The search was prompted by Gonggong's unusually slow rotation, which suggested a gravitational companion had been braking its spin. An earlier set of Hubble images from the 9th of November 2009 was also found to contain the satellite.
Under a prograde orbit model, Xiangliu completes one full orbit around Gonggong every 25.22 days at a distance of roughly 24,021 km. The initial estimate, based only on the discovery images, placed the period anywhere between 20 and 100 days.
Xiangliu's diameter is uncertain. The initial discovery estimate was 237 km, assuming equal reflectivity with Gonggong. Current constraints put its diameter above 36 km at minimum and most likely below 100 km, with an albedo above 0.2 required for the eccentric orbit to have persisted over the Solar System's age.
Xiangliu's color index V-I is 1.22, compared to 1.65 for Gonggong, a difference of 0.43. This gap is among the largest recorded for any binary trans-Neptunian pair; most such pairs show very little color variation between their two components. The cause of the difference has not been established.
Xiangliu is named after a nine-headed venomous snake monster in Chinese mythology known for causing flooding and destruction, who served as chief minister to the water god Gonggong. Both names were approved by the International Astronomical Union's Committee on Small Body Nomenclature and announced simultaneously by the Minor Planet Center on the 5th of February 2020.