The Nightmare Hex is a Hex that is classified as Dark Magic. It fires a dark waving, spinning jet of dark blue and black flames. It knocks out the target for 2 hours and gives the victim horrible nightmares that seem to be real (although it's not real)
It's unknown who created the Hex, although it was created somewhere in the 1500s.
Andreiko Igorobravitch-Used it as one of his common moves during duels and battles
Yaxley- used it on Gryffindor and Hufflepuff students that he didn't like during his Hogwarts years, Alex John, for example, was his favourite target from Hufflepuff
Pandora Lovegood (mother Of Luna)- Probably was defending herself from a few dark wizards
Xenophilius Lovegood-Was using it on several Death Eaters in order to defend Luna
- The Incantations to the hex is both in Japanese and in latin "Noctis" mean Night, "Molum" comes from Malum, which means evil and "Yume" (Yume is in Japanese) means dream or hope or wish