It's hard to manipulate dark magic for those who are as righteous as it can be. However, Dark Atlantette is more of a manifested reflection of Atlantette's fear, especially when she's afraid of the darkness as well as the unknown. Therefore, Dark Atlantette harbors the powers of darkness and the unknown, that may cause anybody else to suffer from the briny deaths that they faced upon. Let alone the fact that Dark Atlantette is a dark construct made up of dark magic, while using an angler fish as a vessel to transform it into an evil doppelganger.