The Shadow Moon, also known as All Souls' Fest and the Night of Shadows, was an event in Malaz City which occurred irregularly (two or three times a century) and was usually accompanied by the appearance of a whole host of ghosts, revenants, shades, and other creatures. According to Agayla, on this one night "every portal, every gateway, every fault between Warrens, all open a crack." Sensible city residents stayed barricaded indoors as people caught out on the streets were known to disappear.
In Night of Knives
During the night of the Shadow Moon in 1154 BS, various forces converged on the Deadhouse due to its alignment with Shadowkeep. These included shadow cultists, Stormriders, and Kellanved and Dancer. The house's guardian, Jhenna, tried to take the opportunity to escape the house's thrall, but was stalled by Temper and entombed by the house.
Kellanved and Dancer succeeded in gaining entry to the house and ascended to High House Shadow.