The Youma were the first monsters of the week to appear in Sailor Moon. They are servants of the Dark Kingdom, sent by its generals to collect energy from humans. Many of the Youma can disguise themselves as humans and work independantly, and they are almost entirely female.
Depending on which general the Youma was working under, each would have different general jobs. Jadeite's Youma tried to collect energy from as many people as possible, Nephrite's Youma would collect energy from a single human at the peak of their lives, and the Youma Zoicite awakened were ancient allies of the Dark Kingdom trapped inside the Silver Crystal and reincarnated as humans.
Balm[]
Balm was a Youma summoned by Jadeite. In her human disguise she set up a forutune telling business. Any student who had their fortune told by her was turned into an unruly servant and had their energy syphoned off. In her Youma form Balm's hair could from into powerful claws. Sailor Moon accidentally stumbled upon her operation and destroyed her.
Castor & Pollux[]
Castor and Pollux are two Youma summoned by Nephrite. They absorb the energy of a young animator driven to prove herself. When unleashed they are able to use Mars and Mercury's powers against the Senshi. When it comes time to defeat the Senshi, however, they bicker over who deserves the killing blow, which gives all three Senshi enough time to combine their powers and destroy the pair. Castor has fire powers, while Pollux has water powers, and they can use them only when their tail is tied (indicating their bond of friendship). They are named after the famous greek heroes and twin brothers of the same name.
Castor & Pollux make an appearance as the bosses of level 1 in the Sailor Moon arcade game.
Kyurene[]
Kyurene was entrusted by Jadeite with a casette tape which could steal life energy. She then promptly lost it, and spent the rest of the episode trying to get it back. In her Youma form she could fly and attack with sound waves, and could turn her fingernails into claws even in her human disguise. Her plans came to naught after her hostage was rescued, the tape was destroyed by Luna, and Sailor Moon turned her sound waves back on her before destroying her in the usual manner.
She appears as a minor enemy in Sailor Moon: Another Story. She is also the boss of stages 3 and 6 of the Sailor Moon Arcade game. Stage 3 even replicates her flight to the Tokyo Tower.
D. D. Girls[]
The D. D. Girls are the Dark Kingdom's last, and strongest, line of defense. They were sent by Queen Beryl to prevent the Sailors from breeching her arctic castle. Through the use of illusions and their vine-like arm tentacles they managed to kill all the Sailor Soldiers aside from Moon, although every one of them died in the attempt.
The D. D. Girls, like most major Sailor Moon villians, reappear in Sailor Moon: Another Story. They pose significantly less risk to the now more powerful Soldiers.
Derella[]
Derella is a youma summoned by Jadeite. She assumed the identity of an idol and then tricked schoolchildren into giving up their energy to become celebrities. In her Youma form she can spit liquid glass to trap people. Sailor Moon uncovered her identity and then shattered her with a Tiara Action.
Flau[]
Flau assisted Jadeite in his plans to gather energy for the Dark Kingdom through the use of a late-night radio program. By sending her flowers to women writing love letters they could absorb the energy of unrequented love. In her Youma form Flau can fire energy blasts from her mouth. Sailor Moon crashed the duo's radio broadcasting setup and sliced Flau in half with a Moon Tiara trick shot.
Garoben[]
Garoben was a Youma summoned by Jadeite. She ran a cram school that was secretly a front to sap the energy of students. In her Youma form she could transform her arm into an axe. Usagi was able to destroy her after Ami awoke to her own power and distracted the monster.
Garoben is the boss of stage 5 in Sailor Moon arcade, where she's still runnign a cram school, but this time she's menacing Umino.
Iguara[]
Iguara was a Youma summoned by Jadeite. She ran a pet shop that sold a new type of pet called chanela. The little rabbitty things smelled pleasant and never ate, but in truth they fed off of the love of their owners, turning them into slaves. Sailor Moon discovered her operation and, after healing the enslaved children, destroyed Iguara. Her death also destroyed all the chanelas.
Kigaan[]
Kigaan was a Youma employed by Jadeite. She drove busses filled with hypnotized girls into an alternate dimension so that she could absorb their energy. After Rei became Sailor Mars she was finished off with a single Fire Soul.
Morga[]
Morga was the first Youma sent to Tokyo by Jadite. She impersonated Naru's mother and began selling magic jewelry that sapped the life out of its wearers. In her Youma form Morga could stretch and contort her limbs and neck. Sailor Moon was drawn to the Youma by Naru's screams for help and, after a little pep talk, she was able to summon up the courage to destroy her.
Petasos[]
Petasos was a Youma used by Nephrite. She gave a park keeper powers over nature and the anger to use them against the development crew trying to pave over the park. Along with being able to summon insects and animals she can also restrain people with her vine hair or with vine pods launched from her hands. She was able to trap Moon and Mercury on her own, but a surprise attack from Mercury was enough for her to get finished off with a Tiara Action.
Thetis[]
Thetis was a servant of Queen Beryl, althrough she had feelings for Jadeite. In an attempt to improve his reputation with the Queen she hatched a plot to absorb the energy of love from couples. Thetis showed a remarkable range of powers for a Youma, from being able to raise and disguise a shipwreck as a functioning cruise ship, making servants out of seawater, attacking with streams of seawater, and stretching her limbs. Thetis was more than a match for Sailor Moon one on one, but after being distracted by the sudden appearance of Mercury and Mars Sailor Moon was able to destroy her.
