Porygon

Porygon is an unusual Pokemon from the Kanto region. It is identified to be a Normal type Pokemon.

Porygon was not known to have an evolutionary stage until the later Generations. In Generation II, it was discovered that Porygon can evolve into Porygon2 when traded away while it's holding an Up-Grade. In Generation IV, it is discovered to evolve even more to Porygon-Z when trading away a Porygon2 while it's holding a Dubious Disc.