To get Mewtwo, players need to defeat the Elite Four, give the Sapphire gem to Celio and journey to the Cerulean Cave. Once Celio has been given the Sapphire gem, Mewtwo appears in the cave.
- Battle the Elite Four
After earning all eight badges, players can battle the Elite Four. After winning, watch the end credits, and start the game again. The player awakens outside of his home and is guided through the islands until he receives the Sapphire gem.
- Surf to Cerulean Cave
Cerulean Cave is located on Route 24. Players surf from the water in Cerulean City and travel down the direct route to the cave entrance.
- Navigate through the cave
Cerulean Cave is a maze filled with strong Pokémon. Players need to work through the maze to the bottom floor.
- Surf to Mewtwo
Mewtwo is standing on a small island in between two rocks. Use surf to reach the island. Walk up to Mewtwo, and press A to initiate battle.
- Catch Mewtwo
Mewtwo can be caught in battle using an Ultra Ball or Master Ball. If using an Ultra Ball, you need to lower Mewtwo’s HP significantly and make it fall asleep in order to catch it.