Dark ankous are randomly and uncommonly summoned during the fight with Skotizo. They are slightly darker variants of regular ankou. If the player kills a dark ankou, Skotizo may randomly summon another. There is a limit of one dark ankou in the room at a time. If a dark ankou spawns on the opposite side of Skotizo from the player, or if the player is attacking an altar, it will wander around the room. If the dark ankou walks near the player and they are attacking Skotizo, it will become aggressive towards them.
Whenever one of the four awakened altars is active, a timer of a random duration is set, which will spawn a dark ankou once it has ticked down.[1]
There is no real benefit fighting dark ankous, so the player should instead focus on fighting Skotizo.
^Jagex. Mod Ash's Twitter account. 16 December 2021. Archived from the original on 24 June 2023. Mod Ash: "[Do you know how the dark ankou at Skotizo works? (...)] Looks like it's off a timer on an open altar, with a random duration on that timer. So "it's random" might actually be the most appropriate answer."