You have to attain the Silph Scope to reveal the ghost. Kill it (LVL 30 Marowak) and then fight a series of Rocket grunts to get to Fuji, who gives you a pokeflute.
you cant
A lot
you cant go underwater in leafgreen!!
cant, only on firered
you cant unless you trade
you cant
HelloSorry to say but you cant trade Pokemon from pearl to leafgreen but you can migrate Pokemon from leafgreen to pearl via the pal park
only ghost types and you cant catch the cubone and the marowak because its part of the story
you cant
you cant.
you cant
A lot
i am very sorry, but you cant...
you have to get it in a event and you cant get it in Pokemon leafgreen or firered
You cant. You get it in the pokemon ghost tower by beating all the team rockets
u cant
You cant