Kamen Rider: Villainesses

I might miss some, let me know. Very little villainesses in the Showa era, here are some monsters I found notable:

Bee Woman
A female bee monster armed with a rapier as her weapon. The end of said rapier contains an ultrasound emitter that hypnotizes sunglass wearing victims. Destroyed by Kamen Rider 1's Rider Kick. She appeared in 2 episodes of the original Kamen Rider series and was played by Nao Oikawa (Kegalesia of Go-Onger) in Movie War 2010 movie.

Doctor Kate
A plumed cockscomb monster that shoots poisonous liquid. She is destroyed by the poisoned Tackle's Ultra Cyclone. Appeared in four episodes of Stronger.

Snake Woman
Snake monster, destroyed by Stronger (Charge Up)'s Super Electro Big Wheel Kick. Appeared in 2 episodes.

Villainesses:
Princess Yōkai/Satan Doll
She can be considered the first villainess. In Super-1, she wore a butterfly mask, she has no interest in Jin Dogma's affairs. She was destroyed by Super-1's Super Rider Horizon Kick.

Staff Officer Witch/Majoringa
A voluptuous sorceress. Assuming the form of Majoringa, she was destroyed fighting Super-1 with the Lightning Sword while praising Jin Dogma with her last breath.

High Priestess Bishium
She appeared in Kamen Rider Black. Bishium became overconfident of herself and tried to convince Shadow Moon that her plans could finally defeat Kamen Rider Black, ignoring advices from her good allies, Darom and Baraom. Bishium held Black so that Shadow Moon can shoot a beam that will rip out Kotaro's King Stone, it destroyed her.

Maribaron
In Black RX, the sorceress of the State from a noble family outside the Crisisians with feelings for Jark. She was killed by Crisis when she objected on his decision to have RX join them. She became Nefaria in Masked Rider, played by an American actress.

Saeko Kageyama / Lobster Orphnoch
In 555, she works as the proprietor of the Clover Bar. Her calling card to her victim is to send them a bottle of wine, which turns out to be their final drink. She enjoys seeing others suffer and comforts them in a somewhat disturbing fashion. Saeko allowed the Arch Orphnoch to completely evolve her, removing all traces of her humanity, and thus became his caretaker after he was defeated by Faiz.

Can Crane Orphnoch be considered a villainess?

Kamen Rider Shuki
In the series Kamen Rider Hibiki, she appears in one episode. All the warriors had motifs of instruments, hers was a harp. When she was young, her entire family was murdered by the villains and become an Oni. She used personal grudge and not the desire to uphold justice and protect the weak as a reason to fight. Unlike the others, the demon face took over her helmet. She ended up killing herself to get her revenge.

Rena Mamiya / Uca Worm
In Kabuto, she is Uca Worm, the first executive Worm. A cruel and clever planner, she is the one who ordered a Worm to capture Juka. Ultimately, she is fatally wounded by Kamen Rider Drake's Rider Shooting twice in their final battle, ending with Uca Worm ultimately dying in Daisuke's arms as a human.

ClayDoll Dopant
In Double, Wakana Sonozaki is the youngest daughter of the Sonozaki family has been secretly raised to become the key element in her father's plans. As Claydoll, she can make gravitational energy shots, as well as the ability to reform her body after it is shattered into pieces. She uses a Xtreme Memory to evolve her into ClayDoll Xtreme to prepare her for the Gaia Impact. After getting the means to invoke the Gaia Impact from Shroud in her final moments, Wakana sacrifices her own existence to bring her brother back via the Xtreme Memory.

Taboo Dopant
Saeko Sonozaki is the eldest and runs the Digal Corporation. As the Taboo Dopant, she can fly and shoot fire bombs. She uses an L.C.O.G and Gaia Memory in its Level 3 to become the R Nasca Dopant to overpower her sister. However, Saeko is forced to go after the Jewel Memory to make herself more powerful than ClayDoll Xtreme, before the Nasca Memory is destroyed. Taboo Dopant sacrifices herself to hold off the Utopia Dopant to give Wakana time to run away, killing Saeko.