How do u get ditto in emerald?

To get Ditto you have to beat the elite 4 then go to the Digger's House, west Fallabor Town. In the back of his house, there is a cave. He will tell you not to go in the cave because it is not safe. Go in anyways, and almost all that will attack you is Ditto at level 37 to any number in the 40's! Keep going through the cave and at the back you will find a fossil. If you chose the Claw Fossil earlier in the game then it will be a Root Fossil. If you chose the Root Fossil you will find the Claw Fossil. (Or you could trade it from Pokemon Fire Red or Leaf Green.)