A flying squirrel/bat monster. It can breathe fire, use its fangs to inject a toxin, and shoot electrical beams from its eyes. It was used to turn Shigeru and other children into vampires. Kohtaro was bitten by Shigeru and during a battle with Musalabisala, he was bitten again. Kohtaro became Bio Rider to create an antidote and get by injecting the fluid. Kohtaro tricked Musalabisala into thinking that he fell under his control. The trick worked, allowing Kohtaro to transform into Kamen Rider Black RX and fight him. Musalabisala had RX in a pinch until Joe threw one of his sais at him. Kamen Rider Black RX used the RX Kick on Musalabisala before destroying him with the Revolcane.