When you first visit Three Island, you'll come across a miner looking for gold in one of the caves. If you return to him after beating the Elite Four, he'll hand over a Nugget, an item that can be sold at high prices.
When you are in the Safari Zone, it counts the number of steps you take to determine the amount of time you have left. Well, if you want to catch a rare Pokémon, but don't want to run out of time, enter the grass, then lightly tap the directional pad. You will change the way you are facing, but it will not count as a step. You can have near-infinite time in the Safari Zone doing this. It is helpful when some Pokémon, such as Chansey, appear in only one section of the Zone.
Every time you encounter a pokemon you have a 1/8192 chance of the pokemon being a different color, this is called a shiny pokemon
When you first visit Two Island, the local Pokemart will be severely limited in the items for sale. As you complete various tasks, more items will become available.
Go to 'Island 4' and go to the bragget house where he asks you what you want to Brag about.
By completing certain tasks, it is possible to upgrade your trainer card a total of four times, from the intital blue to green, bronze, silver, and gold. The upgrades can be obtained in any order, and each one adds a star to your trainer card and upgrades the color.
At the beginning of LeafGreen/FireRed, you can only trade between the two respective versions. However, if you complete a certain task in the game, you can trade to Pokemon Colosseum on the Gamecube, and Pokemon Ruby/Sapphire, the two other Pokemon games on the GBA.
When you have access to Two Island, save the Game Corner owner's daughter, then deliver the package. The grateful owner will open some mini-games that you and your friends can play.