Instructions
Generation I
Start a game in ̶0;Pokémon Red,̶1; ̶0;Green,̶1; ̶0;Blue̶1; or ̶0;Yellow.̶1; Progress through the game until you obtain the Pokedex from Professor Oak.
Go to any Pokémon Center. These are located in all major towns within the game.
Talk to the person at the right counter to enter the "Cable Club." Connect your Game Boy to another player who is at the same place in her game.
Choose to battle or trade Pokémon between the games. You can connect any of the Generation I Pokémon games with one another.
Generation II
Play ̶0;Pokémon Gold,̶1; ̶0;Silver̶1; or ̶0;Crystal̶1; until you have successfully delivered the Mystery Egg to Professor Elm. This will unlock trading and battling between the Generation II games.
Go to any Pokémon Center and head up the stairs to the second floor.
Speak with the clerk at the first counter to enter "Cable Club Trade" or the second counter to enter the "Cable Club Colosseum."
Connect your Game Boy Color to another player's Game Boy Color with a Generation II game.
Trade and battle against your fellow player.
Generation III
Play through ̶0;Pokémon Ruby,̶1; ̶0;Sapphire̶1; or ̶0;Emerald̶1; until you obtain the Pokedex from Professor Birch. Play through ̶0;FireRed̶1; and ̶0;LeafGreen̶1; until you obtain the Pokedex from Professor Oak.
Go to any Pokémon Center and proceed to the second floor.
Talk to the clerk on the second floor to either trade with or battle against another player. Generation III games allow up to four players to battle against each other. Each must have his own game.
Connect to your opponent or trading partner with a Game Boy Advance Link cable. Battle and trade against your friends.
Note that you can only connect ̶0;FireRed̶1; and ̶0;LeafGreen̶1; with ̶0;Ruby,̶1; ̶0;Sapphire̶1; and ̶0;Emerald̶1; after you have obtained the National Pokedex at the end of the game. Until then, trades and battles can only occur between the games of each set.
Generation IV
Play through ̶0;Diamond,̶1; ̶0;Pearl̶1; or ̶0;Platinum̶1; until you receive the Pokedex from Professor Rowan. Play through ̶0;Pokemon HeartGold̶1; and ̶0;SoulSilver̶1; until you receive the Pokedex from Professor Oak.
Head to the second floor of any Pokémon center and speak with the clerk to enter random battles and trading. Your DS will connect to others around the world without the need for a link cable.
Go to the basement of any Pokémon Center and speak with the clerk to enter the "Wi-Fi Club." Here you can connect with your friends by trading friend codes. View your own friend code and enter the codes of your friends from the "Wi-Fi Club" menu.
Select your friend's name from the "Wi-Fi Club" plaza after entering her friend code. You can then select to battle and trade with your friend.