Horrors of Malformed Men (1969)

AKA: Edogawa Rampo Zenshū: Kyoufu Kikei Ningen
Year: 1969
Directed by: Teruo Ishii
Starring: Teruo Yoshida (Hitomi/Genzaburo), Tatsumi Hijikata (Jogoro), Teruko Yumi (Hideko/Hatsuyo),
Country: Japan, Asian Cinema
Language: Japanese (English Subs)
Runtime: 01:39:14
Genres: Mystery, Body Modification, Family, Incest

Plot – Spoilers:
Hitomi is an inmate at a mental institution, haunted by a lullaby and strange recurring images of a cliff and weird people. He escapes from the asylum and follows the distant sound of the same lullaby being sung by a woman on the street. The next day, he visits her at a circus where she performs, but she is killed by an unknown assailant before she can provide further details.

Hitomi is now not only a certified madman but also an alleged murderer and so goes into hiding, traveling along the coast of Japan, hoping to unravel the mysteries that haunt him. His efforts lead him to a recently deceased identical man, and a bizarre island populated with deformed people engaging in various perversions including bestiality and led by a crazy deformed man with webbed fingers.