How do you get to 4 island in Leafgreen Pokemon?

Answer 1

Catch at least 60 Pokemon and then talk to prof. Oak and he'll let u go.
Vermilion city is the dock you need to beat the elite 4 first
first you need to have a national pokedex. to obtain this, you need 60 Pokemon then go to prof.oak then go to one island and talk to celio and he will exchange your tri-pass into a rainbow pass. and he will ask you a favor to find two stones(sapphire and ruby).
you beat the elite 4 then get 60 different kinds of Pokemon then get the new pokedex , go to 1 island and go into the Pokemon center talk to celio and he will ask you to get him a gem, then go to were moltres is (surf to and then past kindle road) there will be 2 team rocket grunts blocking a cave, beat them both got into the cave find the gem and take in to celio he will then give u the pas that will let you explore 4,5,6, and 7 islands
Just beat the elite four and go to Vermillion city as usual. When he asks you were to go, you say 4 island.

Answer 2

you have to beat the elite four, then you will be asked to go there when you go to island one

Answer 3

beat the elite4