After Darth Sidious gifted Darth Vader the planet Moustafar, the Sith Master also gave his apprentice the mask of the long dead Sith Lord Darth Moment, which housed Momen's spirit, believing that the artifact would guide Vader during his studies in the volcanic planet. Vader then set off for Moustafar with an Imperial Architect intent on creating a fortress on the planet. Once a Moustafar, Darth Momen's mask possessed an Imperial Officer, killed the Imperial Architect, and drew a plan to construct a castle for Vader. Momen then explained to Vader that if Vader used Momen's design and built his castle atop a Sith cave that housed a Dark Side Locus, the castle could channel the Force energies from the Dark Side Locus underneath, allowing it to open a door to the Dark Side, which would grant Vader the ability to reunite with his late love Padme Amidala. Over the course of two years, Momen designed and built a total of eight castles, but they all failed, resulting in Vader killing Momen's host body and necessitating the need for the dead Sith Lord to possess a new body. Once Momen's knife and final design was completed, Momen then double-cross Vader and opened the door to the Dark Side, which allowed Momen's physical and spiritual forms to be reunited.