Hoenn Gym

After you defeat the Gym Leaders, Elite 4, and Champion, you will unlock the following legendaries:
 * Latias
 * Latios
 * Groudon
 * Kyogre
 * Rayquaza
 * Jirachi
 * Deoxys
 * Deoxys (Attack)
 * Deoxys (Defense)
 * Deoxys (Speed)

Gym Leaders
Roxanne-

Rustboro Gym/Stone Badge

Pokemon:

Geodude lvl. 12 (Tackle, Rock Throw, Rollout, Magnitude)

Geodude lvl. 12 (Tackle, Rock Throw, Rollout, Magnitude)

Nosepass lvl. 15 (Tackle, Rock Throw, Rock Slide, Discharge)