Stygne was one of the fifty Daniades (daughters of Danaus). In an arranged mass marriage fifty daughters of Danaus married fifty sons of Aigyptos and all but one killed their husbands on their wedding night. Stygne killed Polyktor.
When Erato and the other Danaids who had murdered their husbands they were sent to Tartarus and were forced to carry water from the river Styx in a bowls (or jars according to some) with holes over to a tub which leaks at multiple parts. Erato and the others were told only when they filled the tub could they wash away their sins. The Danaids continue this essentially impossible task to this very day.
Spouse & Lovers
"The twelve sons of a Naias Nymphe named Kaliadne [and Aigyptos]drew lots for the daughters of Polyxo, also a Naias [and Danaus]. The sons were named Eurylokhos, Phantes, Peristhenes, Hermos, Dryas, Potamon, Kisseus, Lixos, Imbros, Bromios, Polyktor, and Khthonios; the girls were Autonoe, Theano, Elektra, Kleopatra, Eurydike, Glaukippe, Antheleia, Kleodore, Euippe, Erato, Stygne, and Bryke."