Hoenn is the third region in the game, obtainable only by beating the Johto Elite Four.
It is located on the left of the reception gate (west of Viridian City). There are pokemon found here that can't be found anywhere else. Some include Absol, Tropius, Feebas, and more.There is also known that some of the pokemon ability and nature change sometimes/45%
There is a map of Hoenn in the game currently.
Grass: Treecko (eventual evolution is Sceptile). Located sometimes in Altering Cave and permanently found in Hoenn Safari Zone (HSZ). Found in tall grass.
Fire: Torchic (eventual evolution is Blaziken). Located sometimes in Altering Cave and permanently found in Hoenn Safari Zone (HSZ). Found in tall grass.
Water: Mudkip (eventual evolution is Swampert). Located sometimes in Altering Cave and permanently found in Hoenn Safari Zone (HSZ). Found by fishing.
1st gym: Roxanne (specialist of Rock types. Has a Mega Tyranitar) Located in Rustboro City.
2nd gym: Brawly (specialist of Fighting types. Has a Mega Lucario). Located in Dewford Town
3rd gym: Wattson (specialist of Electric-Types. Mega Evolution is Ampharos). Located in Mauville City
4th gym: Flannery (specialist of Fire-Types. Mega Evolution is Blaziken). Located in Lavaridge town
5th gym: Norman (specialist of Normal-Types. Mega Evolution is Kangaskhan). Located in Petalburg City
6th gym: Winona (specialist of Flying-Types. Mega Evolution is Aerodactyl (holding a life orb). Located in Fortree City.
7th gym: Tate & Liza (specialists of Psychic-Types. Tate has a Mega Metagross, Liza has a Mega Alakazam) Located in Mossdeep City
8th gym: Juan (specialist of Water/Ice-Types. His Mega Evolution is Mega Gyarados). Located in Sootopolis City.
1st Elite Four: Sidney (specialist of Dark types.She is known to have Mega Tyrannitar.)
2nd Elite Four: Phoebe (specialist of Ghost types.She is known to have Mega Gengar.)
3rd Elite Four: Glacia (specialist of Ice types.He is known to have Mega Abomasnow.)
4th Elite Four: Drake (Specialist of Dragon Types.He is known to have Mega Garchomp.)
Champion of Hoenn: Wallace (specialist of Water types. Has a Kyogre and a Mega Gyarados).