Don’t you just need 2 copies? One to hold the Mewtwos and another to keep doing new games?
Don’t even need a new game. You could clone pokemon by turning the game off mid-trade. My school had a kid that got a Mew from an event, then cloned it for everyone who wanted one.
It became possible in GSC to clone with a single cart. Switch boxes and time a restart correctly during the save and bingo bango, you have a cloned pokemon with whatever item it was holding.
This was awesome for getting extra Master Balls and Rare Candies.
You could clone items in the original games too iirc you would go swimming somewhere near cerulean city and keep going back and forth over the same spot and I think it would buffer overflow the item count for a certain slot in your backpack with a nearly infinitely high number.
You could do it with one copy probably. But this was pre-internet so harder to know about the glitches and such.
I think many people figured out the Missingno shoreline kept some form of “last encounter table” in it, so I wouldn’t be surprised some people may have tried to go there right after Mewtwo to chance themselves at more.
Unfortunately we do have that info nowadays, and we know that doesn’t work.
