One of the strongest Pokémon in the game is Rayquaza, how do you get this Pokémon in Pokémon Sapphire Version?
1. First, you need to have defeated the Elite 4, otherwise it's not even possible.
2. Go to Mauville City and switch your bike to the Mach Bike.
3. Fly to Pacifidlog Town.
4. Then swim (dive at the Pokemon Center) to the right until you encounter a red-haired lady. Then go up and to the left. You should now reach the cave.
5. Continue your way through the cave and end up at the Sky Pillar.
6. You have to make your way through the Sky Pillar. Once you've done that, you'll encounter Rayquaza lvl. 70!
7. Do your best, because catching it is the hardest part if you don't have a Master Ball anymore. So save your game before you battle it!
Good luck!!