I would say Rayquaza or jirachi
it could be rayquaza
Kyogre.
Probably Psycho Boost.
infernape,torterra
Steven Stone is the most powerful trainer in Pokémon Emerald. He can be found in the upper area of Meteor Falls after defeating the Elite Four.
rayquaza
Move Tutors in the Pokemon games from the third generation on can teach the player's starter Pokemon its most powerful type move. The starter Pokemon must have maximized its friendship with the player before learning this move.
The strongest Pokemon on Pokemon emerald would probley be raquaza
RAYQUAZA
Yes, someone can help get a sixth Pokemon in Pokemon emerald. Swellow is a good Pokemon for flying types. Even though they are hard to train, dragon Pokemon make an excellent sixth Pokemon as they are "extra" but very powerful.
You can only get Rayquaza in Pokemon Diamond by trading it from Ruby, Sapphire, and Emerald. The Rayquaza is a very powerful flying dragon type Pokemon.
Get a powerful Pokemon with the Pickup ability and walk around. It should give you rare items such as rare candies.
all of them are in emerald