Monster-of-the-Week

Monster-of-the-week is a fan-created term that refers to any expendable minion who appear in one (or, in some rare cases, two) episodes, serving under one of the more powerful villains to complete some nefarious objective.

Almost always, they are "healed" or die through one of Sailor Moon's signature attacks (Moon Tiara Action, Moon Princess Halation, Moon Spiral Heart Attack, Rainbow Moon Heart Ache, Moon Gorgeous Meditation) with the exception being Regulus or by one of the Sailor Senshi (e.g. Sailor Mars fatally scorches the youma Kigaan as well as two of the Doom and Gloom Girls).

They appear in the anime, manga and live-action series of Sailor Moon "as well as various Sailor Moon video games ". The following monsters-of-the-week exist in the Sailor Moon series:
 * Youma - They are the primary monsters of the Dark Kingdom. They first appeared in the manga, Codename: Sailor V as minions to the Dark Agency, a branch of the Dark Kingdom, which is run by Danburite, before it was defeated by Sailor V. The Youma in the manga, like the ones in the anime, disguise themselves as humans under Jadeite's command until they attack. In the first half of the first season, they were in charge of collecting energy for either Jadeite or Nephrite, which would be lost once the Youma was destroyed. The second half, they were humans turned into monsters, either through the efforts of collecting rainbow crystals or to be used to attack the Sailor Senshi. These specific types were healed and restored to human by Sailor Moon.
 * Cardian - Kept inside cards working for Ail and An to drain energy for the Makaiju. The Cardians are exclusive to the anime and absent in the manga
 * Droid - sent by the Spectre Sisters (Koan, Berthier, Calaveras, and Petz, who were working for Rubeus), to take over crystal points, and later Esmeraude, to fill Tokyo's vulnerable spots with dark energy. One droid, Jakoku, worked for Prince Demande. After a droid's defeat, they would dissolve to dust, leaving behind a gem with the Black Moon symbol, before it turned to stone. In the manga, almost all Droids look exactly the same, and assisted the Spectre Sisters in their missions, including disguising themselves in a crown of people.
 * Daimon - These being possessed things (in manga: living beings; and anime: primarily objects). In the anime, the Daimon would possess an object and take the form with properties of the object and assist in the extraction of the Pure Heart (either directly extracting it, or distracting the Senshi for Eudial as she extracted it). In the manga, Daimons possessed humans rather than inanimate objects, and they were mostly generic monstrous forms. The Witches 5 were considered perfect Daimons in the manga, and all members of the Death Busters were Daimons.
 * Lemures - Who worked for the Amazon Trio and Amazon Quartet. For the anime, they lived in the Dead Moon Circus tent, and awaited to be summoned through their master's shadow to fight the Senshi whenever they tried to foil their plans as seen in Sailor Moon SuperS. In the manga, Lemures were small formless shadow creatures who attacked in large groups.
 * Phage - A normal human whose Star seeds has been taken out and corrupted by one of the Sailor Animamates who work for Shadow Galactica. They are often parody of a Sailor Senshi and their appearances vary depending on their personality, trait or occupation. They only appear in the anime.