>>54398137Pokemon creatures in Gen 1 were designed with a very particular philosophy and concept in mind.
There is a stark difference in both look and powerlevel as well as even rarity between regular animals and yokai/monsters.
Take Pidgey: it's just a bird, evolves into just a bird that has low base stats across the board and no real good moves, is everywhere, and has a high encounter rate.
Then you have Pikachu, which is an early game mon that deviates from the inherent underpoweredness of Normal type as well as the normality of being a regular beast. Ratata really is just a mouse, but Pikachu is more than a mere mouse (reminder that in the following gen, it's added to the Fairy egg group). It has an elemental power, which makes it more special than what would be encountered up to this point, and has a 5% encounter rate alongside that.
And then you have Jigglypuff not long afterward, which despite being Normal type isn't an animal at all, but a weird creature, who eventually becomes able to learn a variety of attacks regular animals typically don't have access to. Its encounter rate is also a low 10 percent to reflect this.
And you have monsters like Mr. Mime and Jynx who cannot be found in the wild at all and defy the look and logic of most other creatures in the game with their humanoid appearance. And they also have access to moves and capabilities that regular animals don't.
The point in adding these My Mom's animals is to create a sense of the other Pokemon being otherworldly and special. Up through Gen III, they still designed this way, explicilty demarcating between rare and powerful yokai vs common and bland and relatively weak regular animals.
