Let’s Kill Uncle (1966)

Director: William Castle
Cast: Linda Lawson, Mary Badham, Nestor Paiva, Nigel Green, Pat Cardi, Ref Sanchez, Robert Pickering, William Castle

Synopsis:

A 12-year-old orphan who has just inherited a fortune is trapped on an island with his uncle, a former British intelligence commander who intends to kill him. A young girl is the boy’s only ally against the sarcastic uncle, who uses hypnotism, a pool of sharks, fire, and poisonous mushrooms as weapons.