HM Dive is acquired relatively late in the game; in "Pokémon Emerald," it is acquired in Mossdeep City. Getting Dive is a simple matter of asking someone for it, but being able to use it requires players to first win the seventh Gym Badge.Continue Reading
To reach Mossdeep City, you need to be at the point in the story where you've dealt with Team Aqua's attempt to steal the submarine by making your way through their hideout. Once you've done this, reach Mossdeep City by following Route 125 to the location.
First visit the Space Center, and speak to the person immediately inside to get a Sun Stone. Next, visit Steven, whose house is in the upper-left corner of Mossdeep City. Talk to him to be rewarded with the Dive technique.
Unfortunately, having Dive and using it are two different things. You're prevented from using it on the world map until you have the seventh Gym Badge. The Gym in Mossdeep has a Psychic theme. The masters are Tate and Liza, who send out a level 42 Solrock and a level 42 Lunatone. Steel, Dark, Ghost and Bug Pokémon all have an advantage over Psychic types.