Who's that Pokemon?さんのイラストまとめ

Venomoth Family (048,049)

This one is pretty hard, if you know about a monster or legendary creature that resembles it's description sure will help
Their designs are based on a Mite (Venonat) and a fuse betwen a Moth and a Morpho Butterfly (Venomoth)
But....

Parasect Family (046,047)
In the real world there are various species of parasite fungus, based on this a lot of fantasy and horror media were created fusing it with magic or alien origins, mostly related on creating zombies

I belive this family are more inspired in the japanese Kodama Myth
The Kodama are forest spirits, there's not a single description of them, but sometimes they are described as humanoid living plants, sometimes they are good, other times they are like demons

Bellosom Family (043,044,045,182)
This one is tricky
Some people says that because of the poisonous atribute in most of the evolution line, they must be inspired in the Mandragora Myth, but i doubt it, because these fictional plants screams when are dugged up~

Crobat Family
(Pokedex 041,042,169)
In a lot of Fantasy media, the bats are related to vampires and common rpg enemies in dark places
Their pokedex descriptions says that one is more vicious and strategic than the one before, like they are part from a vampire Hierarchy

Wigglytuff Family
(Pokedex 174,039,040)
Based on their pokedex info and their shape, the Wigglytuf Evolution line seems to be based in part on the japanese legend of the Moon Rabbit, that's why the ears in Wiggly and the red eyes in Iggly are that way and being tied to lullabies

Once a Kitsune is more older and gain a nine tail is called "Kyubi no Kitsune" and became silver skinned, with god like powers

Ninetales Family
(Pokedex 037,038)
In japanese folklore it's belived that when a Fox (Kitsune) get to an advanced age it grows many tails and learn paranormal abilities, the most prominent is breathing fire.

Nidoking & Nidoqueen families
(Pokedex 029,030,031,032,033,034)
This two families take inspiration on the Toho Kaiju "Baragon" a 4 leged mammal-like monster that is also known as God of the earth because of it ability to dig and travel underground

Sandslash Family
(Pokedex 027,028)
In some fantasy media are sand Golems or elementals that have the ability to harden their skin or make it sharp. This traits fits with Sandshrew evolving in Sandslash.
The same goes with their alolan forms, ice Elementals and golems are similar