For an unknown amount of time the people of Papua New Guinea in area of Sepik region had something that terrified women and children.

These hangahiwa wandafunei (the latter term being an adjective meaning "violent" or "hot-blooded" in a ritually powerful sense) are universally feared, and nothing can vacate a hamlet so quickly as one of these spooks materializing out of the gloom of the surrounding jungle. The reason why even men flee before it is that the spirits of its victims have putatively impregnated the mask. Thus, when an ordinary man dons one of these costumes he feels the "heaviness" of the mask, and the indwelling spirit(s) transform him into a compulsive killer; his own child or brother would not be spared if he came upon them. To this extent, the men are not entirely deceiving the women when they tell them that the hangahiwa are spirits incarnate. Traditionally, hangahiwa wandafunei sought out victims who were alone in their garden or on the forest paths at dusk. Pigs, dogs and chickens were also fair game. After spearing the victim, the offending hangamu'w would escape back to its spirit house. The wearer would replace it with the other costumes and emerge without fear of detection - in time to join the general alarm aroused by the discovery of the body.

Book: The Voice of the Tambaran: Truth and Illusion in Ilahita Arapesh Religion

Wait why would they go around killing people? Was this a revenge thing or ritual sacrifice or what

The men demanded food through the the nggwal "spirit", and used this to get what they wanted. Think of it this way the women, and children thought this a real spirit, and gave it what it wanted. Women were forbidden to know about this secret, and if they caught one they would be scared to ever say thing about it.

Oh, I thought the spirit just went around killing whomever they came across.