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How is this even a question? Gen II has CLONING. Nothing is limited. Want an Espeon and Umbreon but don't want to breed an additional Eevee and raise it all the way up? Raise the regular to max friendship normally, clone it, and level both up at different times.
Want all three starters? Avoid saving until the end of the process and figure out what starter you want your rival to have for the game you stay with (ie. you want your rival to have Totodile so the final starter you choose is Cyndaquil). Choose your first starter, get to the point where can catch another Pokémon, deposit your starter in the PC, switch boxes, turn off the power around DON'T TURN OFF THE P-, and load up a new game. Choose a different starter, catch another Pokémon, the first starter should still be in the PC, deposit the second starter, repeat the glitch, choose your final starter in final new game, you can save now. The other two starters are in your PC, but not in your Pokédex. You have to breed their eggs to get their first stages registered, but evolution will register the other forms. And you'll get bonus experience since they'll have the IDs and OTs of the previous files.
Stones limited in GS? Have Pokémon hold them and then clone them. Worried about coming across a shiny that flees/explodes or sick of dealing with Raikou, Entei, and Suicune? Clone the Master Ball just in case.
