Strange Demon Beast-Man
The Strange Demon Beast-Man unit is led by Bosgun, composed of mutants and animal-like humanoid aliens.
Gynagiskhan
Known as the "Knight of Wind", Gynagiskhan was an insectoid-like horseman with sensitive hearing who used a glaive in battle and manipulate winds up to 100 mph. He brought Kotaro and his friends into the Desert of Fierce Winds where Walter and followers were exiled. After killing Walter, Gynagiskhan battles RX with Reiko's musical necklace disrupted Gynagiskhan enough for RX to kill him with the Revolcane. He returned in the Kamen Rider Black RX movie to assist Deathgaron, United Triplon, and Musarabisara into attacking the Kamen Riders only to be destroyed by a team Rider Kick.
Episode 3
Gynagamoth
A three-eyed green moth monster who based himself at cave for his experimentation to revive the deadly Gaina Moth from extinction, altering their venom so the infected have an hour before mutating into humanoid Gaina Moths. With Reiko, her teacher, Shigeru, and his friends stumbled into it and are trapped within the cave and poisoned as a result, Kotaro attempts to deliver the curse with Gynagamoth attacking him. Using Rideron to hold off Gynagamoth, RX manage to cure his friends before killing him with the Revolcane, causing the Gaina Moths to die out as a result.
Episode 5
Gynamite
A crab-like monster with shape shifting powers who is sent after a girl named Tomoko, who is half Crisisian on the side of her father is about to awaken her powers. Though Kotaro interfered, Gynamite assumes the form of the girl's father to get her, only she uses her Crisisian powers to knock him into his true form as Kotaro arrives and becomes RX to fight him, chopping his pincer off before the monster used his toxic breath on him. Gynamite tried again to take the girl who used her Crisisian powers on him. RX used his RX Kick on Mite before he was destroyed by RX's Revolcane.
Episode 8
Gynabalas
A man-beast type monster with long horns and blue black and white spots over his body who was commanded by Bosgan. Besides attacking with his horns, he also wields a sword in battle. Bosgun had invented a machine that turned people into humanoid animals (mostly pigs). When Gynabalas was sent to obtain a kid who was turned into a humanoid gorilla, he ended up in conflit with Kotaro who became Kamen Rider Black RX, until the kid returned and attacked Gynabala. Joe disguised himself as a humanoid pig version of Kotaro to trickt Bosgun, Gynabalas, and the Chaps into capturing him. When Kamen Rider Black RX arrived, Joe shed his disguise and Kamen Rider Black RX fought Gynabalas, destroying the machine that turned people into animals and returning the people to normal. Kamen Rider Black RX fought with Gynabalas until their fight leads outside of the factory. When Gynabalas managed to hit Kamen Rider with his sword, Kamen Rider called out his Revolcane to disarm Harmful Brass. When Gynabalas's sword was knocked away by Kamen Rider's Revolcane, he used his sword to slash into Harmful Brass's stomach. This seriously injured him and he was destroyed by RX's Revolcane.
Episode 23
Gynakamakil
A black-haired lizard/mantis monster. He can detach the blades on its back to throw them and use them as weapons. He is commanded by Bosgun who accompanied him to attack Kotaro where Gynakamakil manipulated aluminum cans. The second time, Joe disguised himself as a bride to lure out Gynakamakil. While Kotaro and Joe were fighting Gynakamakil, Bosgun used his new sword on the car that Reiko was hiding in and made off with her. When Kamen Rider Black RX caught up to where Bosgun and the Chaps had the other brides, he ended up fighting Bosgun and Gynakamakil. Kamen Rider Black RX became Robo Rider so that Bosgun's sword could not penetrate him, resulting in his destruction. He then followed up with an attack on Gynakamakil. Robo Rider reverted to Kamen Rider Black RX and destroyed Gynakamakil with his Revolcane. Gynakamakil was later revived by Maribaron as part of the Spirit World Kaijin Army.
Episodes 25 & 45
Gynagingam
A long-necked turtle monster. He can bite, launch his head and neck out to constrict enemiest, and shoot sparks from his mouth. He is commanded by Bosgun. Gynagingam put Reiko in the Hospitaland had Utako give a message to Kotaro instructing him to meet him somewhere. When Kotaro arrived at the designated location, Gynagingam attacked him. Kotaro henshined into Kamen Rider Black RX and fought Gynagingam until Bosgun arrived. He transformed into RoboRider, but Bosgun revealed his new sword which was able to penetrate his Robo Rider form, a few strikes from which caused Kotaro to revert to RX form. Kamen Rider Black RX called his Acrobattler and then retreated. When Shigeru and Hitomi were captured by Bosgun, Gynagingam, and the Chaps, a weakened Kotaro fought Bosgun and Gynagingam while Joe freed Shigeru and Hitomi. After Joe was wounded by Bosgun, Kotaro transformed into Bio Rider and fought them. Bio Rider was caught by Gynagingam and turned into water to escape and evade Bosgan's sword. After being disarmed, Bosgun retreated. Gynagingam was beheaded by Bio Rider who reverted to Kamen Rider Black RX and destroyed him with the Revolcane.
Episode 26
Gynaninpo
An ape monster that leads the Devil Beastman Ninja Corps. Gynaninpo wields an extending staff in battle which he can shoot beams from. He can also assume the form of anyone he chooses. After the Devil Beastman Ninja Corps attacked a mountain village and captured its inhabitants, they and Gynaninpo attacked Kotaro and Reika while they were in the woods though they were saved by Joe. Joe infiltrated the building that Bosgun had the prisoners in by disguising himself as a Devil Beastman Ninja, until his coughing gave him away to Bosgun and Gynaninpo. Gynaninpo took out Joe and assumed his form. Gynaninpo sent the Devil Beastman Ninja Corp to attack the place where Kotaro and Reika found the kids taking refuge. Kotaro fought them until "Joe" defeated them and led them to where Bosgun has the prisoners. After Kotaro found the real Joe, Gynaninpo shed his disguise. Bosgun revealed his plans to Kotaro and left as Gynaninpo and the Devil Beastman Ninja Corps fought Kotaro. Kotaro henshined into BioRider and freed the prisoners. BioRider and Gynaninpo fought outside as BioRider destroyed his Devil Beastman Ninja Corps. He then called for Mach Jabba and charged him. Gynaninpo climbed a cliff and attacked BioRider, but he turned into water, attacked him, and knocked him off the cliff. BioRider reverted to Kamen Rider Black RX and used his Revolcane to disarm Gynaninpo before destroying him. Gynaninpo was later revived by Maribaron as part of the Spirit World Kaijin Army.
Episodes 37 & 45
Gynajagram
A tiger-like monster. He can punch, bite, and is armed with small black boomerangs. He is under Bosgan's command to fight Kotaro. Kotaro transformed into Kamen Rider and they fought, Gynajagram using his boomerangs to attack. Then Kamen Rider transformed into RoboRider and shot him. When Gynajagram went to attack RoboRider, he turned into BioRider and attacked in return. When Biorider took out his Bio Blade, Gynajagram also used two boomerangs to fight. When his boomerangs were destroyed by Biorider's Bio Blade, he still attacked with his free hand. Finally, Gynajagram was slashed by Bio Rider's Bio Blade.
Episode 40
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