-Get The National Dex-
To get the National Dex, just beat the Elite Four with at least sixty pokemon in your Dex and after the credits. You'll arive in Pallet Town and Oak will upgrade u and Gary's Dex.

-Trade With Ruby-
To trade with Ruby/Sapphire, you need to fix the network machine on Island 1.

-Gettin The Legendaries-
Zapdos - Get in in the Power Plant like Red/Blue.
Articuno - Get in at Seafoam Island like Red/Blue.
Moltres - Can be found at Island One.
Mewtwo - Can be found in The Unknown Dungeon.

-Gettin The Legendary Dogs-
The Legendary Dogs appear wild anywhere after you beat the Elite Four depending on you starter. You can only find one pokemon in the game depending on the following starters u select:
Suicune : Charmander
Raikou : Squirtle
Entei : Bulbasaur

-Unlimited Time In The Safari Zone-
Go to the Safari Zone and walk into any area with grass and stop. Now touch the D-pad lightly but don't move anywhere. Now you'll see that your player just turned up/down. Now continue to do it in a rotation (ex Left, Down, Right, Up). Eventually u will encounter a pokemon while just rotating in te same spot.