The Bible Of Mysteries

Mora are mostly malevolent folkloric beings associated with sleep that in some form or another can be found throughout Europe.
In Polish folklore, mora are the souls of living people that leave the body during the night, and are seen as wisps of straw or hair or as moths. In certain Slavic languages, variations of the word mora actually mean moth (such as in Slovak language mora or another example is Czech word můra).

In Croatian, "mora" refers to a "nightmare". Mora or Mara is one of the spirits from ancient Slav mythology. Mara was a dark spirit that takes a form of a beautiful woman and then visits men in their dreams, torturing them with desire, and dragging life out of them. Other names were nocnica, "night woman" in Polish, or éjjeljáró, "night-goer" in Hungarian.

In Germany they were known as mara, mahr, mare, in Romania they were known as Moroi. In Slavic countries the terms included mora, zmoras, morava and moroi; in France, such a witch was the cauchemar. Hungarian folklorist Éva Pócs traces the core term back to the Greek word μόρος moros, death.

As in English, the name appears in the word for "nightmare" in the Nordic languages (e.g. the Swedish word "mardröm" literally meaning mara-dream, the Norwegian word "mareritt" literally meaning mare-ridden or the Icelandic word "martröð" meaning mara-dreaming repeatedly). The mare is similar to the mythical creatures succubus and incubus, and was likely inspired by sleep paralysis.

The mora(mara) was thought of as an immaterial being capable of moving through a keyhole or the opening under a door who seated herself at the chest of a sleeping person and "rode" him or her, thus causing nightmares.

The mora(mara) was also believed to "ride" horses, which left them exhausted and covered in sweat by the morning. She could also entangle the hair of the sleeping man or beast, resulting in "marelocks", called marflätor "mare-braids" or martovor "mare-tangles" in Swedish. The belief probably originated as an explanation to the Polish plait phenomena, a hair disease. Even trees could be ridden by the mara, resulting in branches being entangled. The undersized, twisted pine-trees growing on coastal rocks and on wet grounds are known in Sweden as martallar "mare-pines" or in German as Alptraum Kiefer.

"By Niscor"