There's a Pokémon that drowns children. Another freezes travelers to death. One particular Poké crashes into your room at night and devours your thoughts -- but my favorite Pokémon is the one that raises the dead and makes them dance like puppets.
All right, Pokémon don't actually do that, but their spiritual ancestors the yōkai do, or at least did, in the folktales of old Japan. Over the years, yōkai have served as inspiration for many creatures in the Pokémon universe -- albeit toned-down versions -- creating a mixture of myth and pop culture that helps keep the stories alive and reinforces the Japanese identity of the series.
Japanese culture has always been interested in ghost stories and kaidan-"weird tales." This fascination reached its peak in the Edo period with a parlor game called Hyakumonogatari Kaidankai, that challenged participants to tell one hundred morbid tales, extinguishing a lantern after each one. The resulting demand for new stories of hauntings and violence created a boom in kaidan literature, woodblock prints, and folktale collections, many of which focused on yōkai, a category of supernatural monsters that could range from shape shifting animals to cursed humans. Yōkai quickly became an influential pop-culture phenomenon, appearing in books, on screens, and in newspapers. At one point, there was even a yōkai-themed card game known as Obake Karuta, which challenged players to snatch monster cards out of a lineup based on auditory clues. The player who collected the most cards won.
See where I'm going here?
While yōkai and Obake Karuta were not the inspiration for Pokémon, the massive cultural influence of kaidan was bound to seep into a game that featured strange monsters with supernatural abilities. Besides, yōkai are still a common sight in manga and anime, though they are often toned down in the same way that Disney blunted the Brothers Grimm fairy tales, and their portrayal in Pokémon fits this model of removing objectionable material.
Take Lombre, for instance. With his green, slimy skin, turtle-like head, mischievous nature, and the lily pad rain-catcher on his head, Lombre has all the hallmarks of the kappa, a river imp. However, unlike Lombre, kappa were said to kill horses, cattle, and fully grown men, though their favorite prey were unwary children playing by the water's edge. Folktales describe the kappa as an ambush predator, erupting from the water to seize its prey and drag it into the depths. Once the victim stopped struggling, the kappa rammed its clawed, webbed hand into the victim's anus, tore out his liver, and devoured it in a cloud of bloody water -- an attack they seem to have left out of Lombre's move set in Pokémon Pearl.
Developers apparently had no qualms about basing Lombre on a blood-drinking water demon, probably because the portrayal of the kappa has changed greatly over time. Once used as a boogeyman to keep children away from the water, today kappa are corporate mascots or playful friends, as shown in the anime Summer Days With Coo. Instead of their violent tendencies, modern media focuses on the kappa's pranks and odd foibles. Kappa love cucumbers, for instance, and are extremely polite; in fact, one way of defeating a kappa is to bow to him, since he will always return the bow, and in doing so, spill the water from his head plate and become powerless. According to legend, if the human refilled the kappa's head plate, the river demon would be eternally grateful and assist villages with irrigation or medicine.