New celestial bodies are traditionally named after deities, most often Roman. Some obvious choices like Minerva, Vesta, and Juno might require changing the names of asteroids.
Trans-plutionian dwarf planets like Eris, Vanth, and Orcus are named after deities representing darkness, death, mystery or trickery.
Keeping with that idea, but not necessarily with Roman mythology, who would you vote for?
http://www.ranker.com/list/if-you-could-name-planet-x-/admiralcrunch, other,
Nephthys
Egyptian Goddess of night
Phobetor
Roman god of nightmares (image depicts Somnos - a god of sleep)
Osiris
Egyptian God of the Dead
Rahu
Hindu god of eclipses and trickery. According to Wikipedia, in Vedic astronomy, Rahu is represented by a rogue planet.
Latona
A Roman goddess of Primordial Night who gave birth to the sun and moon. She's the equivalent of the Greek Leto who gave birth to Apollo and Artemis.
Erebus
Greek god of primordial darkness and shadow
Ratri
Hindu goddess of night
Liber
A Roman god of mischief - similar to Dionysus
Loki
Norse god of trickery
Eshu
Yoruba spirit of darkness