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Watch The Manster online — it may be available on legal streaming platforms such as YouTube, Netflix, Prime Video, Hulu, Disney+, and others.

An American reporter in Japan is sent to interview an eccentric Japanese scientist working on bizarre experiments in his mountain laboratory. When the doctor realizes that the hapless correspondent is the perfect subject for his next experiment, he drugs the unfortunate man and injects him with a serum that gradually transforms him into a hideous, two-headed monster.