From Steven at his home in Mossdeep City but you can't use it until you've defeated Tate and Liza, the Pyshic Pokemon Gym Leaders :)
I don't think there is a sub, but you can get the tm dive to go underwater.
You don't.
you cant get regigigas on Pokemon emerald its to ew of a Pokemon
trade from leafgreen or firered
in a cave at the town after sootoplis
from boos and from mali
this is impossible!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
There was never any Pokemon events for emereald.
in route 111,114,120 it is common their
Cutter's House in Rustboro
It is given to you by a fisherman on Dewford.
Get it in the contest hall in slateport city.