After you beat the Elite Four.
go to the cerulean cave and catch mewtwo
Go to the cave between Cerulean City and Pewter City.
Cerulean Cave
Cerulean Cave
No
Cerulean cave located near cerulean city.
you can still go to cerulean cave to catch it like in firered and leafgreen
mewtwo is in cerulean cave
Cerulean cave
It's located nearby Cerulean City to reach there go to route 24 use Surf then follow the water down until you reach the cave.
inside cerulean cave near cerulean city.
go to cerulean cave after you beat the elite four and help celio fix his machine on those islands. you go into cerulean cave work your way through that and mewtwo is in there