Nox Aeternus - Die Nacht der Hexen (1987)

A lost extreme splatter film from Liechtenstein about a group of teenagers in the forest who stumble upon a party of witches, who sacrifice children, skins traitors alive and eat their innards. The teens try to escape from the witches, and most end up getting killed in the most indiscriminate manner. The police even get involved but are of no use as they are tortured by the witches. The only surviving teen must take matters into his own hands to stop the evil witches. Having gone insane, he later steals his father's gun, goes on a killing spree and then ends his own life.

Unfortunately the movie Nox Aeternus - Die Nacht der Hexen is not yet available on HBO Max.