Not that I have actively done it but something that I liked about Pokemon White.
Generation only:
- Can only catch Pokemon discovered in the generation of the game you are playing.
- In the case of remakes you can only catch Pokemon from the generation the game came from. example: you can only catch Pokemon from generation 3 in Pokemon Omega Ruby/Alpha Sapphire.
- Also in the case of remakes you can't evolve your Pokemon to forms that didn't exist in that gen. example: you can't evolve Togetic into Togekiss if you are playing Pokemon Heart Gold/Soul Silver or Megaevolve any Pokemon in Pokemon Omega Ruby/Alpha Sapphire.
- It is allowed to use an already evolved Pokemon that was discovered in that generation even if the previous stages of said Pokemon are from past generations. example: receiving from transfer a Togekiss in Pokemon Diamond/Pearl/Platinum.
- Another rule for remakes. You can't taught movements that didn't exist prior to that generation. example: you can't taught roost to Togetic in Pokemon Heart Gold/Soul Silver.
Don't know if is possible in all games, but sounds fun to try.