>>34860412A Pokemon is what it is: A pocket monster, emphasized on the monster part. Despite the fact that the word conveys negative feelings, we know that for a large majority of Pokemon that this isn't the case. Is an adorable Skitty a monster?
What makes a monster in our world? Usually we tag them based on myths, urban legends, and cultural phenomena. Take the Hoenn Weather Trio: Three ancient beasts based off of the ancient Hebrew myths of Leviathan, Behemoth and Zyzz. Also look at the most Ghost-type Pokemon: A majority of them are based on the human fear of haunted or cursed items, like dolls, masks, electronics, even a sword!
But sometimes the monster isn't something that is far out but reminds us of things close by. Birds, fossils, snakes, tortises...theres a biological concept that backs these ones up.
Some of them even are ahead of the curve, referencing themselves to the point where it only makes sense in a world inhabited by these powerful creatures. I'm specifically referring to Pokemon like Ditto, Mimikyu and Mewtwo; Pokemon that exist because of the actions and behaviors of humans that exist within their world.
TL:DR it's more on concept then implementation for me