how do i get that item?

You’ll probably need an HM for that… how many gym badges do you have?

I had trouble with this too. See, what you need to do is grab a Pokemon with a long tail. You hold the end of it's tail, then throw the Pokemon over using it like a grappling hook. Simple as that.

would raichu work?

you become tarzan and swing off the light'sfixturn and land on the thing and grab the item and hope and prey you don't die and break you body....or get a ladder and climb up thier

*light's fixture

Or do a f**king long jump like Mario does

*bulbasaur used vine whip*

Referencing the sunken SS Anne?

Either fly or go to the level above and use strength to push some columns down

Secret door either right or left