SATANICO PANDEMONIUM is a "good nun gone bad" film from Mexico about Sister Maria (Cecilia Pezet), who, after an encounter with the Devil (Enrique Rocha), goes on a mad spree of sexual deviance and bloody homicide.
The main reason for this film's notorious reputation is due to Maria's lusting after an underage boy. This was pretty shocking for its day, but is less so in this era of desensitization via the internet and trash TV. Whether she's inside or outside of the convent, Maria is relentless in her search for debauchery, ultimately committing several murders to cover up her sins. It's fascinating to watch her transform from a Julie Andrews / Audrey Hepburn-type nun, into a full-on, eeevil maniac!
Unfortunately, the ending is a swindle, tacked on to placate the church and the censors...