Regional evolutions and pre-evolutions

Regional evolutions and pre-evolutions of Pokémon are unique to those outside of one or more real-life equivalents to regions from the real Pokémon franchise. These evolutions and pre-evolutions of Pokémon are, by law, prohibited from residing in some regions unless they are allowed on visits or vacations in those regions. They are also immune from evolving (even into a regional evolution) in those regions.

Example
Female Pikachu (or Raichu) outside of the Kanto region are able to give birth to Pichu. However, female Pikachu (or Raichu) in the Kanto reigon can give birth to regular Pikachu. Pichu are, by law, allowed to reside outside of the Kanto region except when allowed to go on vacations there.