To get into the cave, you must defeat the Elite Four, and give Celio which is on One Island the ruby and sapphire. You must get the National Pokedex first. When you have at least 60 Pokemon caught, talk to Prof. Oak, and he will upgrade your Pokedex.
you need to beat the e4 and get the national dex the you have to get the red and blue gems and the guy will let you in.
You have to beat elite 4 to get into Mewtwos cave
Western Cave
You beat the E4 then go to the cave the kid was guarding in cerelun city (the one with misty as leader) He's at the end of the cave.............................................................................................................................................................................................................................................................................................................................................................
On firered, you need to beat every trainer in the game and have rock smash and strengh
give it to celio and then mewtwos cave will be unlocked
theres a pretty good chance most people find there dog by mewtwos cave (cerulean)
beat the E4, but mewtwos in that cave. articunos in seafoam cave, east of cannivare island(the one with the fire gym)
It depends on your Pokemon's level. If it is in the 50-60 range, then train near Indigo Plateau.
Go to the very left of the Pokémon Village. You must have a Pokémon that knows Surf. Follow the stream up to the waterfall and hop out to the right. Walk right and Mewtwo's cave will be there. You have to have defeated the Pokémon League to enter it.
there is none.
No, but it's a sign that you need a hobby.
buy it in the wigglytuff friend areas(after beating rayquaza)