If you think “these Pokémon designs are weird”, they’re not—they have different cultural origins, many of which are linked to Japanese religious folklore. Josh Coyne discussed some of these tales and more about Pokémon cards in Art & Object:
Many of the designs of the Pokémon themselves were heavily inspired by some of these traditional kami. The most notable of these Pokémon is certainly Pikachu, whose core design was inspired by the Raijū: a kami who could take the form of a squirrel-like creature and transform into a ball of lightning.
Among the Pokémon illustrators that Shintoism influenced, perhaps none has had a greater impact on the franchise than Mitsuhiro Arita. Arita illustrated many of the original Pokémon trading cards and, after twenty years, is responsible for hundreds of card designs.