you must catch all 3 legendary bird Pokemon!then have your first sight of MEW the little pink Pokemon is the ancestor of all Pokemon!then he will let you in the cave and make sure you still have your master ball because you have to fight mewto!and you also have to of caught entei,suicine,or raiku!so there you go.try to become a Pokemon master like me!
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that's wrong what you have 2 do is go too 1, 2, 3 island and help fix the network machine then u can go find mewtwo
you can catch mewtwo in cerulean cave in cerulean city but first you have to beat the elite four
Once you beat the Elite Four, you have to go to One Island and talk to Celio. Help him get stuff to fix his trading machine then you can go in the cave. You also have to have caught 60 different kind of Pokemon If this still doesn't get you in then you need to go see a little girl on one of the Islands sorry don't know which one :( and tell her about beating the Elite Four and she will give you a sticker to put on your Trainer Card. Then go talk to the man again.
You have to defeat the elite four and after that it should be open
By beating the elite 4
You will gain access once you have beaten the elite four
Cerulean Cave, nor Cerulean City, was not in Pokemon Emerald. In RBY, it opens up after beating the Elite 4.
you can catch mewtwo in cerulean cave in cerulean city but first you have to beat the elite four
After you beat the Elite Four.
Once you beat the Elite Four, you have to go to One Island and talk to Celio. Help him get stuff to fix his trading machine then you can go in the cave. You also have to have caught 60 different kind of Pokemon If this still doesn't get you in then you need to go see a little girl on one of the Islands sorry don't know which one :( and tell her about beating the Elite Four and she will give you a sticker to put on your Trainer Card. Then go talk to the man again.
You have to get the National Pokédex by catching at least 60 different types of Pokémon and talking to Professor Oak, and then deliver the Ruby and Sapphire stones to Celio on Island One. You can then enter Cerulean Cave.
Complete the elite 4 at least once
You have to beat the Elite Four once.
Beat the elite Four
When you defeat the elite four now you will go to the cave in Cerulean City.
Cerulean Cave can be found just North Of Cerulean heading from Surfing from Route 24. You must have beaten the Elite 4 before you are allowed to enter.
you have to beat the elite four, and get the national dex. then go to cerulean city, go past the nugget bridge, and surf on the water. there is a cave,and its cerulean cave
Mewtwo is in the Cerulean Cave near Cerulean City. To get to Cerulean cave though, you have to get surf, and complete two achievements such as hatch an egg and delete the Elite Four.