To truly beat the game you will need to complete the Pokédex. The regional Pokédex is the same as the Pokédex from the Pokémon Red and Blue games. Once you have 60 unique Pokémon registered in your regional Pokédex and beaten the Elite Four, Professor Oak will upgrade your regional Pokédex to the National Pokédex, which includes all the Pokémon from Pokémon Gold and Silver and Pokémon Ruby and Sapphire, making it a total of 386 Pokémon.
Pokédex Certificates
To obtain the regional Pokédex Certificate you need to catch 150 Kanto Pokémon, excluding Mew.
To obtain the regional National Pokédex Certificate you need to catch 380 of the 386 Pokémon, excluding Mew, Ho-Oh, Lugia, Jirachi, Deoxys, and Celebi.
Catching Pokémon
Most Pokémon from the Kanto region are accessible in the wild as you progress through the game. However, there are specific Pokémon exclusive to each version of the game and you will need to trade Pokémon from the complementary version to complete the regional Pokédex.
Legendary Pokémon
These Pokémon will only appear once, so if you defeat them you won't see them again. Save the game before battling them.
| Pokémon | Location |
|---|---|
 Articuno |
Seafoam Islands |
 Articuno |
Power Plant |
 Moltres |
Mt. Ember |
 Mewtwo |
Cerulean Cave |
Legendary Beasts
You can only obtain one Legendary Beast, depending on which starter Pokémon you chose. You will need to trade with other players for the two you didn't obtain.
| Pokémon | Starter Pokémon |
|---|---|
 Raikou |
Squirtle |
 Entei |
Bulbasaur |
 Suicune |
Charmander |
Available from NPCs
Although not available in the wild, certain Pokémon are available by interacting with characters in the game.
You can only obtain these Pokémon by trading with specific NPCs:
| Obtain | Location |
|---|---|
 Farfetch'd |
Vermilion City |
 Lickitung |
Route 18 |
 Mr. Mime |
Route 2 |
 Jynx |
Cerulean City |
During the game, you will collect an Old Amber in Pewter City and either a Dome Fossil or a Helix Fossil in Mt. Moon. Taking these to the Pokémon Lab on Cinnabar Island will allow you to regenerate Aerodactyl, Kabuto and Omanyte respectively. As you can only collect Kabuto or Omanyte, you will need to trade with another player for the one you didn't obtain.
These Pokémon will be given to you as you progress through the game.
| Obtain | Location |
|---|---|
 Hitmonlee or Hitmonchan |
The Fighting Dojo |
 Eevee |
Celadon Mansion |
Breeding
You only receive either Hitmonlee or Hitmonchan from the Fighting Dojo, and Hitmontop is not available at all. To collect all 3, you will need to breed the one you have with a Ditto to produce a Tyrogue. Once it reaches level 20, it can evolve into one of the 3 evolutions based on his stats:
| Evolution | Stats |
|---|---|
| Hitmonlee |
Attack higher than Defense |
| Hitmonchan |
Defense higher than Attack |
 Hitmontop |
Attack equal to Defense |
There are 5 possible evolutions of Eevee, so you will need to breed the Eevee you are given with Ditto four times.
| Evolution | Requirements |
|---|---|
 Flareon |
Fire Stone |
 Jolteon |
Thunderstone |
 Vaporeon |
Water Stone |
 Espeon |
Level up during the day with high friendship |
 Umbreon |
Level up during the night with high friendship |
Trading
To obtain the National Pokédex Certificate you will need a Pokémon Emerald or Pokémon XD: Gale of Darkness game to obtain the Johto starters and trade them to your FireRed/LeafGreen game.