Ammonite Mutant (23) - An ammonite monster with two brains: a telekinetic brain and a fighting brain. With the first brain, it has telekinectic abilities which it uses to manipulate objects, and it can attack with its tentacles. With the fighting brain, this monster can headbutt. In the first battle, Ammonite Mutant used its telekinectic powers on oil drums to attack Kamen Rider BLACK. He punched off its head which turned into a small ammonite. It was found by a boy named Shigeru (who was visiting the grave of his pet Pochi) who named it Marumo, eventually learning of its psychic power and brought it whatever it needed. With the High Priests were going to punish Ammonite Mutant for losing his head, Bilgenia appeared and revealed that Ammonite Mutant had two brains as the fighting brain emerges, intent to find its missing head. When Ammonite Mutant appeared, Kotaro got Shigeru to safety. Ammonite Mutant caught up with Kotaro and Shigeru at Pochi's grave. As Shigeru ran, Kotaro became Kamen Rider BLACK and fought Ammonite Mutant. Shigeru ran into Bilgenia as Kamen Rider BLACK split its second head open just as Bilgenia appeared with Shigeru in his arm and threw its head back at Ammonite Mutant and its psychic powers are active once more. Battle Hopper attacked Ammonite Mutant and Kamen Rider BLACK used it to attack the rock that Ammonite Mutant had control of. Kamen Rider BLACK killed Ammonite Mutant with his Rider Kick (which also removed the psychic head from it again) and its head awakened Shigeru before disappearing.