>>14303602Assuming you're talking about event Pokemon, Pokemon like that already have their data on the game cart, but the .pkm file used to summon that data and give it moves, stats, etc. isn't
That's why you could Action Replay a Genesect or Meloetta in Gen V, or a Arceus (or hell even the Azure Flute) in Gen IV, Jirachi and Deoxys in Gen III, Celebi in Gen II, and Mew in Gen I