Get Aerodactyl
To get Aerodactyl, go to the house to the right of the Museum in Pewter City. You will need to have "Cut". Talk to the scientist and he will give you the Old Amber. Take it to the Lab on Cinnabar Island and let the scientist bring it back to life.
100% success rate. 

Get National Dex
Once you have beaten the elite 4 and have more than 60 pokemon in the pokedex, go to Pallet Town and see the Professor. He gives you and Gary the National Dex, which allows you to view the entries of all 386 pokemon.
Submitted by pokemongamer. 100% success rate. 

Mystery Gift
Go into any pokemon center and go to the clipboard by the shop clerk. Go to it and you can put 4 words. Put in the words "Link Together With All". The shopkeeper will notice this and give you access to the Mystery Gift System. Now save your game and turn it of and when you go to re-load it will be right below "New Game."
Submitted by pokemongamer. 100% success rate. 

No More Buying Awakenings!
After you get the Pokéflute, use it in battle when a Pokémon from your side is asleep. It will awaken so you don't need "Awakening" anymore. You can use it as much as you want!
Submitted by GR0UD0N. 100% success rate. 

Get Zapdos
To get Zapdos, go to the Pokémon Centre beside the Rock Cave. From the Pokémon Centre, go up until you reach water. Surf to the Power Plant and go inside. Find your way around, and at the end you will find Zapdos.
88% success rate. 

Complete the Pokedex
To complete the pokedex, you will need to trade with other games, Pokémon Ruby/Sapphire, Pokémon Colosseum, and Pokémon Leaf Green.
80% success rate. 

Access Mystery Islands 1-3 and 4-7
To be able to access the first 3 mystery islands, you must defeat all 8 gym leaders. To access mystery islands 4-7, you must then defeat the elite 4 to acquire the Rainbow Ticket.
Submitted by pokemongamer. 75% success rate. 

Get Jirachi
Do these things before you do the rest or this will not work.

1. Defeat the Elite 4.
2. Achieve the Ruby and Sapphire (in game items) and give them to Celio on One Island.
3. Get the Pokemon Colosseum Bonus Disc.
4. Have the Gamecube GC to GBA Link Cable. Turn on the GC with the Pokemon Colosseum Bonus Disc. Link the Disc with a Ruby/Sapphire game pak. Transfer Jirachi to the Ruby Sapphire game pak. Trade with the Ruby/Sapphire for Jirachi!

Catch Deoxys (<- =left,& -> = right)
Go to any Poke Mart. On the desk, there should be a square memo. Press the A button on the memo,and a questionnaire pops up. Put in the words "LINK TOGETHER WITH ALL". The man will notice and you should now recieve Mystery Gifts! Save and turn off the game. Turn it on, and under New Game It should have the Mystery Gift option. (In real life) Go to "Pokemon Rocks America!" and get the Aurora Ticket. (Back in the game) Go to the 2nd floor of any Pkmn Center and talk 2 the man in the green hat. Save and turn it OFF. Go 2 the port in Vermillion City and talk 2 the sailor and now you can go 2 Birth Island! Go there and save. Approach the Triangle and press A. Press <- 5 times, & down 1 time. Press A.Press -> 5 times, & up 5 times. Press A. Press -> 5 times, & down 5 times. Press A. Press up 3 times, <- 7 times, and press A. Press -> 5 times. Press A.Press <- 3,down 2. Press A. Press down 1 time, <- 4 times. Press A. Press -> 7 times, then press A. Press <- 4 times down 1 time. Press A. Press up 4 times, press A. Get ready to battle Deoxys!
Submitted by GR0UD0N. 56% success rate. 

Get Running Shoes
To get the running shoes all you have to do is beat the Pewter City gym and go talk to the scientist on the right of the city.
Submitted by pokemongamer. 50% success rate. 

Multiple Attempts at Catching a Legendary Pokemon
When you are close to a Legendary Pokemon and want to catch it, save the game just before you battle it. If you accidentally make it faint, just reset the game and try again.
Submitted by GR0UD0N. 25% success rate. 

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