The Death Busters come along in Sailormoon S. The group consists at first of Kaolinite, Professor Tomoe, and the Witches 5. Further on we realize that Hotaru is also a part of this group, with the sleeping form of Mistress 9 within her body. The Death Busters are after pure hearts in order to awaken Mistress 9 and to revive Pharoah 90.
- - - - - - - - - - /// Kaolinite

Kaolinite is the first sent out to find pure hearts. She
had a crush on
Professor Tomoe, and though it's obvious, Tomoe never figures it out. Kaolinite at first
wore a red outfit, but
the
senshi destroyed her and her altered self was unveiled when Tomoe reincarnated
her. Viluy always makes fun of Kaolinite for liking
Professor Tomoe, and Kaolinite hates Viluy in
return. Actually, Kaolinite doesn't have much of a relationship with
the Witches 5. She harbors a lot of
animosity and bitter thoughts towards them. She
never quite belonged with the rest of the
Witches 5. After her reincarnation, she didn't do
much else to
further the Death Buster cause except help around Professor Tomoe's house.
Later Kaolinite actually achieved quite a lot, her hard work going unnoticed by Tomoe. She found out Usagi was Sailormoon, but Sailorvenus dressed up as Sailormoon and tricked her. At the end, she caught Chibiusa for Mistress 9, but Mistress 9 zapped her against an electric barrier, killing her (again). Kaolinite was simply happy because Professor Tomoe had recognized her hard work for the first time. Uranus commented on how easily the Death Busters betrayed each other.
- - - - - - - - - - /// Eudial

Eudial is quite the villain, managing to attain the two talismans from Neptune and
Uranus, finding out the senshi's identities, and nearly succeeding in killing them if Venus
hadn't interrupted. Eudial uses the attack "Fire Buster," which is more powerful than
Sailormoon's attack. She definitely does the
most out of the Witches 5.
She also was a mentor to the other witches that were still training. She trained Mimet and Tellu and the rest of them, mainly because she was older and knew more than they did. Eudial was appalled when Mimet made fun of her failures and mentioned that she wasn't needed anymore. Eudial couldn't believe that none of them remembered how she taught them all they knew. Eudial is also very good on the computer, and is a fast typist. She always searches for her victims on the computer and figured out Uranus and Neptune's real identities that way.
Unfortunately, when she got the talismans, Pluto appeared and took them away from her. Then Pluto got the last talisman which was on top of her staff, and brought Uranus and Neptune back to life. The Holy Grail was formed and Eudial and Sailormoon went after it. Sailormoon got it, and Eudial was blasted out of the Cathedral that they were in. She ran into the car, and drove to the Witches 5 center. But unfortunately for her (and the Death Busters, because she had valuable information about the senshi), Mimet, the next witch in line, took out the car's breaks, and Eudial went flying off a cliff. Witches 5 became Witches 4.
- - - - - - - - - - /// Mimet

Mimet doesn't quite care for her work; she thinks more about finding famous actors
to be her boyfriend and always chases after good-looking men. She reads a lot of manga while she's on the job, but never really
gets in trouble, probably because she's Tomoe's favorite. He's
always the nicest to her, and whenever she'd
start crying, he
would always comfort her.
Mimet killed Eudial because she was getting fed up with Eudial's failures. It was cruel since Eudial acted as Mimet's mentor for a long time. Mimet was also killed by the next Witch, Tellu. (We're starting to see a pattern here.) She had transferred herself into a machine that put her into a huge screen and made her more powerful. But while she was in the machine, Tellu pulled the cord, and Mimet was gone forever. Witches 4 became Witches 3.
- - - - - - - - - - /// Tellu

Tellu worked through plants. Her Grand Master
Plan of Doom (tm) was to sell plants which attracted the pure hearts of
the people that bought them. When the plants
grew and matured, they would suck out the pure hearts.
Tellu ended up catching hundreds of pure hearts in her lab, but the senshi found her with Pluto's sleuthing. She took a plant seed and created a giant demon plant to fight off the senshi. The plant attacked anything that had a pure heart, including the senshi and the pure hearts of all the people around them. Unexpectedly, the pure hearts somehow migrated towards Tellu and the plant attacked her instead, swallowing her whole. Poor girl didn't even last more than one episode. Witches 3 became Witches 2.
- - - - - - - - - - /// Viluy

Viluy
used electronics and computers to get pure hearts and she was bound by bracelets that
kept her alive. She attempted to steal pure hearts from the students at Mugen
High School, and saw Ami as a rival. When the senshi
were at Mugen High to investigate, she introduced herself to Ami, mentioning that they scored the same mark on the last exam. She took Ami to
a lab and showed her a mini universe made by
science club.
Viluy is self-absorbed and vain. When Ami told her that not all smart people are natural born leaders and that they must understand the heart of poor academics, Viluy rebuffed her by saying she was too kind and that in science, the important thing was logic and it was unnecessary to understand the human heart. She declared that Ami didn't sound like the kind of student who makes such high marks in school.
Viluy's plan was to suck the pure hearts out of the exam-takers in the school through computers. Her weapon of choice were Nano-robots: tiny computers loyal to her command. She'd yell "Mosiac Buster!" and little black electric bits would come flying out of her hands, controlled by the bracelet on her left wrist. These surrounded her target and stabbed their body until they eventually left nothing but that person's pure heart. Unfortunately for Viluy, her bracelets were broken by Sailormoon's attack and went berserk, the Nano-robots chewing her alive instead. Ami quietly said, "You're the one that said machines don't need minds." Witches 2 was down to one.
- - - - - - - - - - /// Cyprine & Ptilol

Cyprine
and Ptilol are twin witches acting as one who are powerful when together
and almost defeat the senshi. When the senshi were fighting these two synchronized
as one, the situation looked bleak for the
senshi. All until Mercury fogged up the area, and the two witches were separated.
When they were by themselves however, Cyprine and Ptilol weakened. They died by accidentally shooting each other. Jupiter and Venus lured them towards each other in the fog, and they both attacked at the same time. When the two senshi jumped out of the way, they ended up attacking each other. They only lasted for one episode, and marked the end of the Witches 5.
- - - - - - - - - - /// Professor Tomoe

Professor
Tomoe, Hotaru's father, runs the show until Mistress 9 is revived. He's good for
laughing like a mad scientist ("BWA HA HA
HA HA!!"), playing very twisted
games of Twister, and casting dramatic shadows
around. He also makes the daimon eggs for the Witches to attack with.
Before Professor Tomoe became the head of the Witches 5, he was a normal scientist, showing other professors an experiment that he constructed. Hotaru was leaning on the glass to look at it. Suddenly, something went wrong, and the place exploded. Everyone died except for Professor Tomoe. Tomoe was devastated that he lost his daughter, but a bright light arrived and told him he could restore Hotaru's life. Tomoe didn't care if there was a catch or not, so he agreed immediately.
A daimon took control of Tomoe's body and Mistress 9 was sealed into Hotaru's, in exchange for her revival. On episodes 124-125, the real (ugly) daimon came out of Tomoe and Uranus and Neptune destroyed it, returning Tomoe to his regular self.
- - - - - - - - - - /// Mistress 9

Mistress
9 is the enmity that was sealed into Hotaru's body. She swallowed Chibiusa's pure heart
and took total control of Hotaru's body, killed Kaolinite (for the
second time) and made a base at the place formerly known as Mugen High, a
prestigious school which Hotaru, Haruka, and Michiru attended. She took the Holy
Grail from Sailormoon (rather, Sailormoon gave it to her) and put it
into a power chamber for Pharaoh 90, destroying it in the process.
Mistress 9 has the whole hair thing going for her. She's got super long hair and uses it to effectively strangle people. Mistress 9 is bad ass and is a master at manipulating people, using the fact that Usagi didn't want to kill Hotaru to trick her many times.
Though Mistress 9 ended up taking over Hotaru's body, Hotaru's soul was still alive. Hotaru recalled all of her loved ones and gathered the strength to overpower Mistress 9, destroying the evil (and destroying her own body while she was at it). Then Hotaru became Sailorsaturn in order to fight Pharaoh 90 and eliminate it completely.
- - - - - - - - - - /// Pharaoh 90
I don't quite know what Pharaoh 90 is. It really only appears for an episode and a half, and it doesn't play much of a role other than being The Evil Bad Guy of Doom that the senshi have to defeat for the general good. It aims to lead earth into a state of darkness, vanquishing all the light in the world.
We never see Pharaoh 90's face, if it even has a face. It's a reddish blob of energy that comes crashing down to earth to bring much destruction and unpleasantness. It doesn't talk either, just makes psychotic laughing noises. Sailorsaturn and Sailormoon go into the core of Pharaoh 90 and destroy it from the inside, of which afterwards, Sailormoon is left standing in the sunlight with baby Hotaru in her arms.