You have to have Grass to beat The first the you have to you lose after that
No its not an HM in leafgreen.
beat the elite four once
train your Pokemon that's it.
Beat the elite four.
You have to beat the Elite Four once.
all you have to do is not get beaten
beat the elite four and your starter has to be a bulbasaur
nothing
go to One Island
You must beat the elite four first, then you can enter.
You have to beat the elite four and complete your pokedex.
The same you can do in Fire Red.Read my answer to that here:What_can_you_do_after_you_beat_the_elite_four_in_pokemon_fire_red