So your'e playing emereld, that is one of my personal favs!
Emereld: go to battle frontier with the boat at lilicove center
after the eliet four you can go and get a legandrr Pokemon called deoxyes
You can get [email protected], access entry to the Battle Frontier via the S.S. Tidal, catch the traditional three legendary Pokemon Rayquaza, Kyogre, and Groudon, if you haven't already done so catch the three Regis, obtain a new feature to your pokedex[national dex], access Safari Zone's expansion project where it is chocked full of Johto Pokemon including Gligar, Stantler, Houndour, Mareep, and Spinarak(There are many more), rebattle Gym Leaders that have new Johto Pokemon you can't catch at all(Example:Later on, Roxanne's Kabuto evolves into a Kabutops and Wattson's Mareep cn eventually turn out to be an Ampharos), acuire the Mystic Ticket which takes you to Navel Rock with a Lv.70 Lugia and Ho-oh(holding the item Sacred Ash, an item that fully revives any fainted Pokemon in your party and refills PP usage), obtain the Aurora ticket, a ticket everyone wants--it takes you to Birth Island and the Famous Deoxys Puzzle and the actual Pokemon Deoxys, and to put an added twist if you already caught [email protected], mix records with a friend who has an Eon Ticket to get a second [email protected], and the other Legendary Bird. Oh, and also be sure to trade Pokemon with a friend who has Ruby or Sapphire, because you can't catch Meditite, Surskit, Roselia, Zangoose or Lunatone, and complete your Hoenn Dex. Once that's completed, talk to Professor Birch and choose either Chickorita, Cyndaquil, or Totidile, and be sure to trade with Pokemon XD:Gale of Darkness, Colleseum, FireRed and LeafGreen to complete the entire pokedex and get that Pokemon Diploma after showing the Gamefreak Game Designer your pokedex in the Cove Lily Motel in Lilycove City. Also, the Fossil Maniac dug the Desert Underpass where wild Whismurs, Loudreds, and even Dittos inside and at the very end the Root Fossil or Claw Fossil--whatever fell into the depths of the sandstorm's sand after the Mirage Tower was completed(Note: The Mirage Tower appears every other time you enter the sandstorm after you beat Flannery; You'll also need the Mach Bike to get past the holes in the ground). I would also take the time to raise any weak Pokemon so you can conquer the Elite Four lots of times(Hint:The Elite Four is an excellent source of money; Be sure to stock up). The TV ad commercials for the Energy Guru, the Lilycove Department Store Clearance Sale and the Game Corner's Service Day will not change; however, there is one new commercial about the Blend Master at Lilycove's Contest Berry Blenders(I've tried going against the Blend Master and he gets targets every time, and the blender goes to roughly about 150-200 mph, and he's the only guy you can blend berries and get Gold PokeBlocks, only they're oh, so hard to get and I have about two Golden PokeBlocks after ten tries). A cave located past the Sudowoodo in the Battle Frontier(Use the Wailmer Pail on the funny looking tree;it'll attack and turn out to be a level 40 Sudowoodo)that contains a Rare Candy and a couple of other items also happens to be the only nest for the one-and-only Smeargle. Also, another thing, some people rumor you can get the Old Sea Chart for the ultimate legendary Pokemon--Mew--by defeating the Frontier Brains and earn all the gold symbols from them
you can complete your pokedex (200) and talk tp professor Birch and you'll go to the johto region. battle Steven in cave(Meteor falls i think),go and beat Battle Frointer,and complete pokedex
SOURCE: my personal experiance ^_^
I did not get your question so hope i am right.