This female alien is a Dark Spawn queen who managed to escape the Banished Realms long ago thanks to the help of Bowser and Hades. although, neither the pooh or Spongebob series ever refered Misstress 9 as a darkspawn queen. In the orginal series of Sailor Moon, she is the Sovereign of Silence, and the one commanding Doctor Tomoe.
Tomoe's daughter Hotaru was chosen to be the one possessed by Mistress 9, who then commanded him to extract Pure Hearts to find the Purity Chalice so she could awaken her master, Pharaoh 90. Once Sailor Moon got the Purity Chalice, Mistress 9 commanded Tomoe to extract Pure Hearts to feed to her. Eventually, Kaorinite brought her Rini, and she ate her Pure Heart and awakened in her true form. She then killed Kaorinite with a lightning bolt, as she did not need her anymore. She sent Tomoe after Sailor Neptune and Sailor Uranus when they entered, resulting in Germatoid leaving Tomoe and being killed by Sailor Uranus.
Mistress 9 tricked Sailor Moon and the un-possessed Doctor Tomoe into giving her the Purity Chalice, and she used it to summon Pharaoh 90, destroying the Purity Chalice. However, Hotaru was able to fight her from within, and overpowered her with her memories of her father and Rini, destroying her completely.
Role in the Series
Despite her apparent demise, her soul was found by Bowser and reformatted into a Dark Spawn Lord in order for her to aid him in his schemes to take over the universe. She also wields a dark version of Kairi's flower keyblade, due to her being a dark magical girl and all. She prefers not to wield the weapon, prefering to let others to do the work for her. She has not appeared yet in the Spongebob adventures series. as mentioned before, Mistress 9 not ever refered to as a dark spawn lord in neither series.