You Have To Go To The Team Rockets Ware And You'll Get Inside Also It's In Five Island
You need to find the two passwords...
in both firered &leafgreen articuno is of 50lv
you get him in the cave next to the manshion on the right
at your next door neighbors house
next to your house in pallet town
Go to the next town.
Press the A button to continue to the next part of the text.
Firered and leafgreen both can catch different Pokemon but there pokedex is the same, here is some examples: magmar only in leafgreen not firered, oddish in firered not leafgreen, ekans in firered not leafgreen, bellsprout in leafgreen not firered, pinsir in leafgreen not firered.
Both are not in leafgreen or firered.
i recommend scizor because onix exist in both versions and therefore possible for both firered and leafgreen to have steelix. But, only firered possesses scyther and therefore, better for it
Fuschia city next to the Pokemon center.
In the game corner in celadon city.