Press 1 to pause game play, then press Z, C, Z, C, Plus two times, Minus two times, Plus, Minus, C two times, Z two times. Press 1 to resume game play. Spyro or Sparx will say something to confirm correct code entry. Press Plus to switch to Dark Spyro (As if you were changing elements).
Note: If you enable the code while in the realm of the Chronicler (Spyro’s “dream”), you will not be able to change into Dark Spyro until you return to the real world.
In order to be able to do this, you first have to beat the story mode. When you have beaten story mode, go to the main menu and select extras. Load the save file with your completed game. Click on “dragon challenges” and beat all five of them. When you are successful the game will tell you that you have unlocked Dark Spyro. Go back to the main menu, load your game again and save it. Use the the element change button until you reach Dark Spyro (it’s the last one in the elements sequence).