Where Is Three Point Pass?

The Three-Point Pass is located right next to the Frigid Sea, on the Crown Tundra's eastern side. It can be reached by going through the cave at the Giant's Foot.

Where can I find Regidrago?

Regidrago can be found in the Split-Decision Ruins, in the Three-Point Pass area of the map. In order to catch it, you'll need to have already caught Regirock, Regice and Registeel.

Can I get both Regieleki and Regidrago?

Once you've added these three Legendary Pokemon to your collection, you can move onto the fourth set of ruins, called the Split-Decision Ruins. These ruins will allow you to encounter and capture either Regieleki or Regidrago, but not both (you get to choose between them).