|This article is about a/an kaijin in Kamen Rider Black.|
It was first seen when the Gorgom High Priests became Grand Mutants.
Stag Beetle Mutant appeared in the form of a landlord when Gorgom used a state of the art condominium and control braces to secretly have any adult tenants wearing it give their lifeforce to their monsters while the children were exposed to knock-out gas. Receiving that info from a boy named Ryou, Kohtaro infiltrates the building to find out what is going on as they end up in an underground pasteur run by Gorgom. After the alarm is set off, Kohtaro henshins into Kamen Rider Black when Bat Mutant makes off with Ryou and goes after Bat Mutant only to be attacked by Stag Beetle Mutant. When Kohtaro find Ryou, he ends up in a trap set by the Grand Mutants and Stag Beetle Mutant. Kohtaro transforms into Kamen Rider Black and fights them. During the fight, Shadow Moon arrives and reveals the purpose of their pasteur to create more Gorgom Mutants before he attacks Kamen Rider Black. Kamen Rider Black tricks Grand Mutant Baraom into attacking the control board for the bracelets freeing the people. Kamen Rider Black then fights Stag Beetle Mutant while Kyoko and Katsumi get the people to safety. Shadow Moon sets the pasteur to self-destruct as Kamen Rider Black fights Stag Beetle Mutant. Kamen Rider Black manages to break off one of Stag Beetle Mutant's pincers before he killed him with the Rider Kick.