The Pokemon games are filled with monsters that inhabit the world alongside humans, but a few of them were actually created by man as well and each one has its own story of how they came about.
As we learn from Professor Ash at the beginning of the first Red and/or Blue games, "This world is inhabited by creatures called Pokemon. For some people Pokemon are pets, others use them for fights," and it seems like other folks decided to create their own.
Where the monsters came from originally is another story in itself, as the games don't provide a ton of lore on the world's past and how humans and the 'mons relationships have evolved over the years, but it's safe to say they've been living cooperatively for some time.
Of course, the most well-known man-made Pokemon would definitely be Mewtwo, as we learned in the Mewtwo Strikes Back movie, but there are a few others whose origins are just as interesting.
As we mentioned above, we learn in Mewtwo Strikes Back that it was created in a lab by Dr. Fuji with the help of Team Rocket, before breaking away from their control and starting a whole heap of trouble.
Considering in the movie it is literally able to control and turn back time, it's safe to say it's probably one of the most powerful creatures on this list.
Baltoy & Claydol
These evolutions were originally clay statues, according to their Pokedex entries, but were given life when exposed to a "mysterious ray" which definitely makes it a possibility that this species was actually created by some ancient alien visitors, rather than human beings specifically.
Banette is another one that doesn't seem to have been created by human hands specifically. According to its Pokedex entry, the Pokemon was brought to life by a "dark, ghostly energy" that seeks out the child who abandoned it.
Luckily our own old toys don't have this capability (that we know of at least).
The loveable Castform was originally created by scientists in Ruby and Sapphire, but since you can find it in wild areas in later games, it's safe to say the weather-sensing cutie pulled off an escape of its own.
This mythical Gen 5 monster was constructed from ancient fossils by Team Plasma, similar to how Aerodactyl came about. It definitely looks more like a combat mech than your traditional 'mon, but we would expect nothing less from the Unova's region militant Pokemon liberation front.
Golett & Golurk
These Ground/Ghost types origin story actually pulls directly from old folklore on the golems they represent. According to the Pokedex they were originally created out of clay (just as in our world) to protect people back in the day.
Golurk is a powerful Pokemon now as it is, but this taste of backstory just has us wanting more info on how they lived with humans in the past, as we mentioned before.
First off, Magearna just looks like something that was artificially made. It resembles a human form, but according to the Pokedex, it was created "more than 500 years ago," and since it looks like a person, it's a fair bet to say people created it as well.
Porygon, Porygon2, & Porygon-Z
Porygon and its variants actually only exist as computer data created by scientists, allowing it to live in cyberspace. How any of them are able to battle Pokemon in the physical realm though, is something that hasn't really been explained, yet.
An Upgrade Disc turns regular old Porygon into Porygon2, which can then be turned into the final Porygon-Z form using the Dubious Disc.
Trubbish & Garbodor
These Pokemon are literally trash, but before you accuse of being too mean to them, consider that they are actually made out of big piles of garbage.
The Pokedex says Trubbish was created from a "chemical reaction" between the trash and some noxious industrial waste, bringing them into being.
Voltorb & Electrode
This one is a bit tricky, since there's nothing in any game outright stating that these electric 'mons were actually created by man, but the fact they were found at the same time Pokeballs were first invented does make it seem very likely.
H/T: Screen Rant