Things You'll Need
Instructions
Trading Mewtwo in Pokemon Silver
Connect Game Boy Color link cables into the sockets on the left side of each of the two Game Boy Color systems. Players can play any Game Boy Color Pokemon game (Red, Green, Silver, Yellow, etc.). Turn the system on, and both players should go to a Pokemon Center. Talk to the nurse and heal all of your Pokemon.
Access the PC in the Pokemon Center to ensure that a player has Mewtwo in his party. The other player should have a Pokemon to trade for Mewtwo in his party as well.
Talk to the receptionist of the Cable Club Trade Center located on the right side of the Pokemon Center, to enter trade mode. Both players must speak to the receptionist at the same time. Select the "Trade Center" option when prompted. Save the game when prompted and move to the table in the room, then press "A."
Move the cursor up or down, and press "A" when Mewtwo is highlighted. A dialog appears asking you if you are sure you want to trade. Select "Trade," and you will now have Mewtwo in Pokemon Silver.
Finding Mewtwo in Pokemon SoulSilver
Defeat all of the Kanto gym owners -- in Pokemon Silver and Pokemon SoulSilver, "Kanto" is the first region in which you play.
Acquire the Master Ball needed to capture Mewtwo by visiting Goldenrod Radio Tower and matching all of the numbers in the tower's radio program, the "Lucky Channel." After defeating all of the Kanto and Johto gym owners, you can also talk to Professor Elm in New Bark Town to gain the Master Ball.
Find Mewtwo standing deep in Cerulean Cave. This will not be a random encounter, and you can walk directly to him. Mewtwo is at level 70, so you will need a party of Pokemon that are at least at Mewtwo's level or higher. Attack Mewtwo until its health is low, and then use the Master Ball on it.
Take Mewtwo to a Pokemon Center and speak to a nurse to heal all of the Pokemon in your party, and then save your game.