In FireRed and LeafGreen you can get the 3 dogs depending on your starter Pokémon. Here are the steps:
WARNING: There is a glitch in the game and if you let the Pokémon use Roar on you, it will disappear from the area section on the Pokédex and you will never see it again.
How to unlock:
Once you have beaten the Elite 4 and have more then 60 Pokémon in the Pokédex, 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 Pokémon.
You have to have gone to the second island. Your Pokémon have to trust you enough and you have to have the one of three starters.(only the one you started with can learn these moves. (Frenzy Plant, Hydro Cannon and Blast Burn)
There are places in the game where important people/Pokémon have stood at one point. If you use the Itemfinder on the EXACT spot where they were, a special item will be found which is usually very rare. You cannot find these items any other way.
How to unlock:
For each 25 times you enter the Hall of Fame, she'll add a new doll to the collection in her house on Four Island. She'll stop after adding a total of eight dolls.
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 first visit Two Island, the local Pokémart will be severely limited in the items for sale. As you complete various tasks, more items will become available.
How to unlock:
Go to 'Island 4' and go to the bragget house where he asks you what you want to Brag about.
How to unlock:
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 Pokémon Colosseum on the GameCube, and Pokémon Ruby/Sapphire, the two other Pokémon games on the GBA. Defeat the Elite Four, then retrive both the Ruby from Mt. Ember and the Sapphire from Five Island Rocket Warehouse, then give them both to Celio.
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.
Every time you encounter a Pokémon you have a 1/8192 chance of the Pokémon being a different color, this is called a shiny Pokémon
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. Also if you have a Pokémon that knows sweet scent you can use that without taking time up.
When you use an item on one of your Pokémon outside of a battle, such as a Potion, the Pokémon will either move closer or away from you in the short intermission sequence. How far the Pokémon moves depends on how much it likes you. If it does not move at all, it feels neutral. You can also take your Pokémon to daisy in Gary's house and ask her.
You don't need to find one Pokémon of each gender in order to breed them. You simply have to put your Pokémon of choice and a ditto into the daycare center. After a short while, the old man will tell you that they found an egg, and when it hatches, it will be whichever Pokémon you matched up with Ditto.
On Island 5, there is an area to the northeast called Gorgeous Resort. There are 2 wealthy trainers you can face. They are named Lady Jacki and Lady Gillian. Lady Jacki gives you $10000 if you beat her ($20000 with Amulet Coin) and Lady Gillian gives you $9800 ($19600 with Amulet Coin). The Pokémon they use also carry expensive items. Jacki's 2 Pokémon carry Stardust, Gillian's 2 Mareep have Stardust, and Gillian's Flaafy has a Nugget. Just use Thief or Covet to obtain these items.
In the Gamecorner in Celadon City, go talk to the man at the far right Slots. He will give you 20 free coins. Talk to the man on the slots beside him. He will give you 20 free coins, also. Go to the left side of the Gamecorner. Talk to the guy that looks like a fisherman, and he will give you 10 free coins. There are also hidden coins on the ground so use the item-finder or press
on every tile.
There's a woman that lives along the Water Path that's looking for a Heracross. If you catch one and bring it to her, she'll measure it and give you a Nest Ball as a reward. Each time you bring her a taller Heracross, she'll give you another Nest Ball.
Apparently, the folks in the Game Corner don't hold on to their coins very well! By using the Itemfinder or looking by yourself, you'll find that many spots in the Game Corner have some number of coins lying on them. If you find them all, you'll find 200+ coins!