How do you get the three regis in Pokemon pearl?

To catch Regirock, Regice and Registeel in Pokemon Pearl, you must:

1. Catch the legendary Legendary Pokémon Cresselia.

2. Go to the top left of the map, there will be a temple near a large body of water.

3. Enter and go downstairs, there will be three puzzles.

4. Place a Pokemon type matching the statue of the regi next to the statue.

5. Solve any of the three puzzles.

6. Fight one of the Regi: Regirock, Regice or Registeel.

7. Catch the Regi once you defeat it.