Queen Metallia

Queen Metallia is the real power behind Queen Beryl's throne in the Sailor Moon universe. She is an amorphous energy being who is the true mastermind of the events in the first season. Like all arch-villains in the Sailor Moon universe, she is a descendant of the final arch-villain Chaos.

Manga

When Prince Endymion & Princess Serenity were to be wed, Metallia took adventage of those on Earth who despised the union. Such a person was Beryl, whose affections for Endymion were preyed on by Metallia. After the war, Metallia was sealed in the South Pole and placed in supended animation. By the present day, Metallia managed to return Beryl to her service and ordered her to find the Silver Crystal so it could be used to free Metallia.

After Endymion was captured, Metallia entered the young man's body to use as a suitable host, letting Beryl die in battle. After Sailor Moon was forced to kill Endymion and then take over life, Metallia was freed to resume her evil. But she was eventally destroyed by Sailor Moon.

Anime

Much like the manga over with a few exceptions. In the anime she eventually became powerful enough to resurrect on her own and then absorbed Beryl to gain a physical form for the final battle.

Live Action

Unlike the manga, Metallia lacked a personality. Beryl originally intended to the use the Silver Crystal to control Metallia, but learned the gem's power only makes Metallia stronger to the point Beryl could no longer control the Youma's actions. In a vain attempt to stop Metallia in her tracks, Endymion took the creature into his body. But it has nightmarish results as Metallia merged with Endymion and then used him in an attempt to force Sailor Moon to use the Silver Crytal's power. The monster's plan suceeded, but Sailor Moon eventally gained control of the gem's powers and used them to destroy Metallia for good.