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. Kotaro ended up bitten by Shigeru and during a battle with Musalabisala, he was bitten again. Kotaro became Bio Rider to get the injected fluid out of him. Kotaro tricked Musalabisala into thinking that he fell under his control. The trick worked, allowing Kotaro to henshin 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. He returned in the Kamen Rider Black RX movie to assist Deathgaron, United Triplon, and Gynagiskhan in their attack on the Kamen Riders only to be destroyed by a team Rider Kick.