After you venture on all of the Sevii Islands, bringing the Ruby and Sapphire to Celio at the Pokémon Net Center on One Island, one of these legendary Pokémon will roam all over the routes in the Kanto region. If you hear the wild battle music in a higher pitch, that means you have encountered the roaming Pokémon. The roaming Pokémon you encounter is on Level 50 and will flee on the first turn. If you have the Master Ball, it would be the time to use it. If you don’t, have any Pokémon use Mean Look to prevent escape but don’t let the opponent use Roar to force you away from battle. Depending on your starter, only one of these will roam in Kanto. If you started with Bulbasaur, Entei will roam. If you started with Charmander, Suicune will roam. If you start with Squirtle, Raikou will roam. ... https://www.youtube.com/watch?v=BCIcWeJt2yc

After completing your adventure on the Sevii Islands, return to Viridian City and enter the gym. This gym has a maze with items and arrow tiles that make you spin. You’ll battle a few trainers as you navigate the maze. Once you solve the maze, you’ll take on Giovanni once more. Giovanni uses Ground type Pokémon. Nidoqueen will use Body Slam to paralyze targets while Nidoking will use Thrash to repeat for 2-3 turns then become confused. Both Rhyhorn will use Scary Face to slow down opponents and the Rock Blast for 2-5 hits. After winning, you’ll receive the Earth Badge and a TM26 (Earthquake). Earthquake is a Ground type move that strikes everyone else on the field and can strike those who use Dig. ... https://www.youtube.com/watch?v=t2Ii_3TFE-k