Queen Metallia

Metallia was Beryl's higher-up. Queen Serenity sealed her away in the Silver Millenium. Beryl attempted to gather energy (specifically from the imperium silver crystal) in order to revive her. Eventually, the Negaforce (Metallia) fused with Beryl for the final battle with Sailor Moon. Sailor Moon gathered power from all the sailor scouts and killed Beryl, also destroying Metallia.