At the time of writing, over 800 Pokémon exist, their influences ranging from shrubs to supernatural entities stretching back eons into Japanese lore. Many are based specifically on Yōkai, strange and grimly comic creatures native to Japan that, like Pokémon, have been recorded in illustrated encyclopedias and playing cards.
Witness this parade of horrors: a head of long black hair that hides a wet, toothy mouth, smiling faces hanging from a tree and swaying with soft laughter, sentient umbrellas that sport long red tongues and a single staring eye (as seen in Nioh), and rotten lumps of flesh that dance on moonlit nights.
These bewitching beasties are the cursed ancestors of Pikachu and his silently screaming cohorts. Take, for example, Grass/Psychic type Exeggutor, a lumbering palm-tree that has up to six expressive humanoid faces. Its origins can be linked to a Yōkai named Jinmenju, or the human-face tree.
Source: Eurogamer The haunted origins of Pokémon