Julia (Marga Lopez, Even the Wind Is Afraid) has been hired to be the governess for Silvia, a rich young girl who cannot connect with her father (Joaquin Cordero, Dr. Satan), who only cares about his new wife (Norma Lazarenko, Survive!) Silvia claims that she has only one friend, Hugo, who everyone else sees as a stone statue in the middle of the courtyard. But when Hugo starts doing her bidding, she may be more correct than anyone could believe.
While a Mexican film, this feels like a Gothic along the lines of The Turn of the Screw or The Innocents. This film is considered one of the classics of Mexican horror cinema and for good reason. It has a thick atmosphere fraught with tension that it delivers on. It was also remade in 2009, in case you feel like hunting that down.
You can watch this on YouTube.