From Bulbapedia, the community-driven Pokémon encyclopedia.
In the Pokémon world, a great deal of advanced technology is shown to be used by humans. Among this technology is the ability to create artificial Pokémon—Pokémon that have not emerged naturally but have been created, either through experiments or indirect means.
These Pokémon, other than being artificially created, are no different from natural Pokémon. They can breed, evolve, be found in the wild, be captured and be trained just as ordinary Pokémon would. Even these Pokémon have DNA which draws from the genetic code of Mew, the supposed ancestor of all other Pokémon besides these.
Known artificial Pokémon
#088 Grimer and #089 Muk
Human pollution is the indirect cause of the formation of Grimer.
Grimer (and consequently Muk), according to several Pokédex entries, was created from human pollution in a stream which was exposed to x-rays from the Moon. This would make it the first (by Pokédex number) Pokémon to emerge due to involvement from humans. Because of the nature of its development, Grimer is highly toxic and uses Poison-type attacks.
#100 Voltorb and #101 Electrode
Voltorb takes on the appearance of a Poké Ball.
Voltorb (and consequently Electrode), according to several Pokédex entries, first appeared at the company where modern Poké Balls were developed. While it is not known why, Voltorb looks strikingly similar to the red and white device, and this likely indicates some level of human involvement. It has been speculated to be a conscious form of energy, a theory supported by its unstable nature.
#137 Porygon, #233 Porygon2, and #474 Porygon-Z
Porygon can exist as computer data in cyberspace.
Before the discovery of Golett, Porygon was thought to be the first Pokémon created deliberately. It is the first Pokémon deliberately created using modern technology, as the result of an experiment by the Pokémon Lab in Kanto. Silph Co. possesses a report on the Pokémon, calling it the first "virtual-reality Pokémon". It is made up entirely of computer data and programming, and is able to exist in cyberspace. According to some Pokédex entries, there is copy-protection data embedded in the program to prevent illegal reproduction. Also, Porygon does not breathe. Its Pokédex entry in Pokémon Yellow speculates it may be capable of space travel; however, this and other abilities are limited to what is included in its program.
Porygon possesses two evolutions, both possible through artificial upgrades. Porygon2 evolves from Porygon when it is traded while holding an Up-Grade. According to some Pokédex entries, it is designed to work in and explore space. However, its Pokédex entry in Pokémon Platinum states it is unable to reach and explore other planets. Porygon2, unlike Porygon, is not limited to what is contained in its program - it is capable of learning.
Porygon2 evolves into Porygon-Z when traded holding a Dubious Disc. It is apparently a modification of Porygon2, designed for travel between different dimensions. However, it did not work as planned and exhibits erratic behavior. Its body and head are in awkward positions, and it is capable of displaying emotion.
Mewtwo is a powerful legendary Pokémon which is the result of gene splicing experiments using the DNA of Mew. According to logs found in the Pokémon Mansion in Kanto, Mew "gave birth" to Mewtwo after an embryo had been developed. This is inconsistent with Pokémon traditionally being born from Eggs. It has a somewhat artificial appearance, most notably the tube protruding from the back of its neck. Like Mew, it harnesses powerful psychic energy. However, Mewtwo's power was amplified to exceed Mew's power in an effort to create the most powerful Pokémon ever created.
Castform was created by scientists and can change forms with the weather.
Castform was created by scientists at the Weather Institute in Hoenn. It was created to help the scientists predict the weather - because of this, it has the ability to change its form and type with the weather condition.
Banette is a plush doll that was thrown away and was possessed by Shuppet.
#568 Trubbish and #569 Garbodor
Trubbish's, and consequently Garbodor's, Pokédex entries says it was created when a garbage dump accidentally had a chemical change of some sort.
#622 Golett and #623 Golurk
Golett and Golurk were apparently created by an ancient civilization to protect people and Pokémon alike.
Other Pokémon influenced by humans
Some Pokémon that formed naturally are shown to be altered in some way by human involvement.
Deoxys is said to be a virus which fell from space while attached to a meteor. Once on Earth, this virus was mutated by accidental exposure to a laser beam which transformed it into a Pokémon. Its DNA remains unstable and it will mutate further when exposed to certain sources of extraterrestrial radiation.
#412 Burmy and #413 Wormadam
Wormadam donning the Trash Cloak
Burmy create outer cloaks out of their habitat. This may be composed of natural materials, as seen in its Plant Cloak or Sandy Cloak, or of artificial building insulation as seen in its Trash Cloak. Burmy can change its cloak depending on the area it is used to battle in.
Female Burmy evolve into Wormadam, which retain the last cloak it had as a Burmy. This may be the artificial Trash Cloak. If so, it will be a Bug/Steel-type Pokémon.
Spiritomb were once 108 separate entities whose sins caused their spirits to be bound together into the Odd Keystone as this Pokémon. The Keystones were then separated from the Hallowed Tower, which triggers Spiritomb's release.
Rotom has the ability to possess artificial machinery. These include toasters, washing machines, refrigerators, electric fans and lawnmowers. These allow Rotom to learn moves of different types and change its base stats, while its Ghost typing is lost and substituted with a type characteristic of the possessed object.
Genesect, a legendary Pokémon, was a different Pokémon many years ago. However, in Unova, Team Plasma reconstructed it from a Fossil with the goal to create the most powerful Pokémon ever. N cancelled the project due to his belief that a Pokémon modified by science would lose its pureness. One scientist, however, kept working on the project in secrecy, disagreeing with N's decision to cancel it. The scientist equipped Genesect with a metallic body, a cannon behind its head, and items known as drives which change the type of its signature move, Techno Blast.