You have to beat the elite four and complete your pokedex.
You can find the Cerulean Cave in the northwest corner of Cerulean City in Kanto in Pokemon LeafGreen. The cave contains the Pokemon Mewtwo.
There not in cerulean cave.
in cerulean cave.
back of cerulean cave
Cerulean cave
Go to Cerulean Cave.
Cerulean Cave.
He is at the end of cerulean cave.
In Cerulean cave in Pokemon firered and leafgreen
At the end of Cerulean Cave.
Mewtwo is found in cerulean cave.
You have to beat the Elite Four once.