There are 151 Pokémon in total, but you'll never get them all without hunting down the rare ones, evolving them in various ways, and trading with your friends. Here's everything you need to know to catch 'em all.
Using Poké Balls
You'll get the vast majority of Pokémon by catching them in the wild. There are four ways to get into random confrontations with Pokémon: walking in tall grass, surfing on water, exploring caves, and fishing. When you run into one, the process is always the same: Weaken the Pokémon as much as you can without knocking it out, then try to catch it using a Poké Ball (or any other type of Ball). Paralyzing, Freezing, or putting a Pokémon to Sleep also makes them easier to catch, and is a necessity for Pokémon like Abra that will run away if not somehow stunned.
Wild Pokémon differ drastically from area to area, so use the Poké Finder charts in each area of the walkthrough to see what Pokémon are available, and how frequently they appear.
Evolving your Pokémon
Many of the 151 Pokémon in your Pokédex can't be caught at all, and will need to be obtained by evolving other Pokémon. Pokémon evolve in one of three different ways:
Experience: Pokémon gain levels as they gain experience, or EXP. Most Pokémon evolve when they reach a predetermined level. Since EXP can only be gained in battle, you'll need to spend many hours leveling up your Pokémon to evolve them. You can try catching the evolved forms themselves, but they tend to be rarer and harder to catch than the base forms, and many evolved Pokémon (like Beedrill and Butterfree) never appear in the wild. Evolved forms tend to be stronger, but don't learn techniques as quickly as their unevolved forms.
Elemental Stones: There are five kinds of Elemental Stones, and 16 Pokémon that can be obtained when you use a Stone on their unevolved forms (only 2 of these, Raichu and Wigglytuff, may appear in the wild). You can use the Stones at any time, but beware: While the evolved forms may have much better stats, they usually lose their ability to learn new moves, with Eevee being the only exception. Before you use a Stone, look up that Pokémon in the Pokédex and make sure they already know every skill you want them to learn.
Trading: Four Pokémon (Alakazam, Machamp, Golem, and Gengar) can only be obtained when their previous forms are traded with friends. These final forms also never appear in the wild, so if you can't find someone to trade them to you'll never get your hands on them. These are also some of the most powerful Pokémon in the game. Unlike Pokémon that evolve with Stones, traded Pokémon continue to learn the same moves, so there is no reason not to trade them off as soon as you can. Just make sure you get them back!
Trading is an important strategy for filling your roster. Keep in mind the following things when you trade:
- You do keep the Pokédex entry for a Pokémon after you trade it away. So by trading a Pokémon to a friend you both get credit for having caught it, regardless of whether he trades it back or not.
- You do not get credit for the earlier evolutions of traded Pokémon. So if your friend trades you his Venusaur, you'll still be missing Bulbasaur and Ivysaur. When trading Pokémon that are rare but also have evolutions (such as starters and the fossils), trade them at every stage of their evolution (and then trade them back if necessary).
- You'll need the appropriate Badge to control traded Pokémon. If you think you can streak through the game with a friend's super-powered Pokémon, you'll be in for a nasty surprise when it just falls asleep at the start of every battle. Each Badge increases the level of Pokémon you can control successfully by around 10, so don't try to get ahead of things. If you're determined to cheat, you can trade your Pokémon to a friend and have him or her teach it TMs and HMs you don't have yet, and then trade them back. Sneaky.
- Traded Pokémon gain EXP about 50% faster. So if you're trying to level up a lot of Pokémon, you may want to trade them to your friends and have them do the training for you. However, if you try to just trade them over to a friend and then trade them back, you'll find that the boost is gone. The Pokémon has to be away from its original trainer to receive the bonus.
The ones you can't get
Catching all 151 Pokémon by yourself is impossible. No matter which version you have, there are Pokémon you simply won't be able to get unless you trade with friends. It is possible to get them all by trading between just the Red and Blue versions (provided someone plays it twice to get the third starter and the third Eevee form), but adding a Yellow player to the mix makes things easier. While there are no Pokémon exclusive to the Yellow version, Yellow players can easily get all three starters as well as rare Pokémon like Farfetch'd and Lickitung.
If you have friends who are starting new Pokémon games at the same time you are, agree beforehand who will get what in places where you're forced to chose between two or three Pokémon. Have one player get the Dome Fossil (Kabuto) and the other get the Helix (Omanyte), one get Hitmonlee and the other get Hitmonchan, and decide who will evolve their Eevee into what. Then trade them all back and forth to fill out both players' Pokédexes.
In addition to the 150 you can get by catching, evolving, and trading, there is a secret 151st Pokémon called Mew that was only officially available at Nintendo events but is also obtainable through the use of cheats and/or glitches. For more information on getting Mew see the Mew glitch page.