Zirconia

Zirconia is the ringmaster of the Dead Moon Circus, and is Queen Nehellenia's right-hand servant. This is the original depiction of the character created by Naoko Takeuchi.

Dream Arc
Zirconia communicates with Queen Nehellenia and delivers her orders to the Amazoness Quartet. When Sailor Saturn and Sailor Chibi Moon begin to break through Zirconia's influence on the Quartet, Zirconia captures all of them, imprisoning the Quartet inside four magic balls and Saturn and Chibi Moon within two shards of broken mirror. She sends the objects through the mirror to Nehellenia. When the Sailor Soldiers confront her, she rises into the sky and grows in size, but the Sailor Soldiers use Sailor Planet Attack to defeat her. Zirconia escapes into Nehellenia's mirror, but when Sailor Moon follows, she only finds Nehellenia. Following Nehellenia's apparent defeat in the mirror's world, Zirconia reappears in the mirror and claims that the Queen of the Dead Moon will not die yet and that the Dead Moon will triumph yet before disappearing, reviving Nehelenia in the process.

Biography
When the Dead Moon Circus arrived, Zirconia commanded the Amazoness Quartet in the invasion. When it seemed their loyalties were wavering, due to Sailor Saturn and Sailor Chibi Moon's words, she trapped the Quartet in the Amazon Stones and trapped Chibi Moon and Saturn in mirror shards and placed them in Nehellenia's mirror. Zirconia fought the Senshi and did lethal damage to Sailor Moon and Tuxedo Mask, but they were rescued by Pegasus. She tried trapping them in a nightmare, but Tuxedo Mask was able to snap them out of it. When Nehellenia was harmed, Zirconia called for the Dead Moon Circus to retreat to Elysion, and she was not seen since.

Etymology
Zirconia is named after zirconium, a chemical elemental metal which implies falseness (Genuine Cubic Zirconia).

Trivia

 * In the manga, Zirconia is the only antagonist who's fate remains unknown. After a fight between the Sailor Senshi and Nehellenia, Zirconia has the Dead Moon Circus retreat to Elysion and Zirconia is never seen again.
 * It is possible Zirconia was an avatar of Nehellenia, acting in her stead until Nehellenia began taking direct actions herself, causing Zirconia to either no longer exist, or return to being a part of her queen. The fact that Nehellenia's hag form is identical to Zirconia can support this. This does seem to happen in the anime.