Regice
Return to the frozen Almia Castle to find the ice spire that hides the secret of Regice. Look for the blue ice spike rising from the floor in the Mismagius room and have a Pokemon use a "Burn 5" attack on it. After being burned with such a powerful fire technique, Regice will reveal itself and wander around the room. Walk your Ranger into Regice to instigate the battle sequence to capture it. Magmortar is one of the Pokemon that knows "Burn 5."
Regirock
Bring a Pokemon that has the "Crush 5" ability to Vien Forest and search for the lone brown vertical rock spire. Use "Crush 5" on the spire to smash it. Regirock appears from the rubble and walks aimlessly through the forest. Bump into Regirock to start the capture process. The sharklike Garchomp is always equipped with "Crush 5."
Registeel
Keep an eye out for a silver bullet-shaped pillar deep on the right-hand side of the Krokka Tunnel. Have a strong Pokemon use the "Cut 5" attack on the statue to slice it in half to reveal Registeel. It is not an aggressive Pokemon unless is approached in battle. Gallade's blade arms are perfectly equipped for the "Cut 5" ability.
Capturing Techniques
You will need to encircle each Regi 20 times in quick succession with the capture device to keep Regirock, Registeel and Regice for your team. Quickly draw small loops around the golem that you are facing to fill the capture meter. Each Regi uses strong attacks that will damage or break the line, forcing you to restart the looping process. Regirock stomps and throws rocks on top of the capture line, Regice creates ice shields to protect it from your loops and Registeel keeps its guard up with a pair of sparking spheres. Lift the stylus from the screen when the Regi attacks and you will capture it will little trouble.