You can't catch Mewtwo in-game in Pokemon Diamond.
You cannot catch Mew in "Pokémon Ruby."or you can get mew-two in fire red or leaf green.
Mt.Moon
I don't think you can catch MEW without a action replay. But you can catch MEW2 in Pokemon Fire Red or Leaf Green. You CAN'T cach mew without an action replay, but you can trade mew-two from the other games to the newer ones
The Cerulean Cave
YOU JUST COItinue what your doing
sadly,no
You catch Mew-Two
Mew and Mewtwo are not found anywhere in the Sinnoh region.
no because there isn't a mew-three just mew and mew-two sorry
You can't catch it at Pokemon Pearl, you'll have to Transfer it from LeafGreen/FireRed or trade it with SoulSilver/HeartGold
i dont know beat the game i gues
You can only using a Nintendo mystery gift.