Use master balls. Use a ton of ultra balls and put them to sleep or paralyze but master balls are your best bet since leaf green is harder than its original counterpart
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You may have to train your Pokemon to at least level 20 or use a electric type like pikachu you can catch it in viridian city but its rare to find.
it's rare to find a moonstone
by cheat
you can catch sudowoodo and smeargle
Magmar is VERY rare and you have to find it past kindle road but not inside the mountain