There is a big demon in fairy tales such as Shan Hai Jing, whose real body and prototype are fireflies. Does anyone know its name and origin?

This is probably a monster named "Nightmare", which appeared in Monkey King Thrice Defeats the Skeleton Demon and the Monkey King vs Bai Gujing starring Dicky Cheung and Chen Haoming. He can enter anyone's dream, in which he is invincible. Tang Priest and his disciples passed by the Flame Mountain, and the Monkey King wanted to learn from Princess Iron Fan (the Monkey King and Niu and Princess Iron Fan were the founders of Bodhi, and Niu wanted to make Princess Iron Fan pregnant because of an affair. Therefore, the Monkey King called Niu Wangmo the eldest brother and Princess Tiefan the eldest sister. He borrowed a banana fan to put out the fire. He didn't want to meet the nightmare of wanting to eat Tang Priest, so he entered Tang Priest's dream. Niu and Princess Tiefan decided to jointly deal with Anvil because they missed the wonderful time with the Monkey King, but in the dream, no one was an opponent. In desperation, they thought of finding his real body and defeating him in reality, but when they approached the rootstock, they fell into a dream spell and entered the dream again. Tang Priest used his quick wits to close his eyes and read the Guanyin Sutra. Everyone closed their eyes and read the Guanyin Sutra together, which cracked the magic of the anvil demon and defeated the dream. It turns out that incubus is a big glowing firefly! ! !