Other pokémon you catch can be left with relatives or friends (but not Prof. Oak) or stored on the PC system.
If you want to switch pokémon in your party for stored pokémon you must visit a pokémon centre.
Before deciding which pokémon you want to join forces with on your journey, there are a few things you should consider.
Firstly, each trainer can have no more than TWELVE pokémon. If you already have twelve and you want to catch another, you must write out one of your existing pokémon.
Excessive switching of pokémon you own is frowned upon—remember, a pokémon's for life, not just a gym battle.
Secondly, if you're going to challenge the gyms, you should be mindful of the pokémon the gym leaders have. You can challenge the gyms in any order you want, so make sure you start with the pokémon who're strong against the gym you plan to challenge first.
We recommend starting with no more than three pokémon at your disposal, so that you can make the most of catching more on your journey.
You can of course be a 10-year-old on their way to get their first pokémon if you like. If you want to challenge a gym, though, you must have at least three pokémon with you.
Now, with those points in mind, you can choose your partner pokémon. This is usually your first pokémon, but it does not have to be one of the starters. You could catch a pidgey in the city centre, or a goldeen in the stream behind your house. It's up to you.
Before you set your heart on one, though, there are a few rules:
1) You can only have unevolved pokémon in your party. That means no metapod, no pidgeotto, no raichu, etcetera. This rule ignores baby pokémon; you can have a pikachu, clefairy, jigglypuff etcetera if you wish.
2) You can have no more than than ONE starter;
3) And no more than ONE baby.
4) You CAN NOT have any legendaries, without exception.
5) Special dispensation must be sought from admins for the following pokémon:
6) No shiny pokémon!
Apart from those rules, you've got a free reign to get any pokémon you want—it can be from any region you like.
Once you're decided which pokémon you want to journey with, you should decide on its personality and its nickname, then create it on the PokéSim, ready for battle!
