Walkthrough
As you complete The Sacred Bonds Of Sovereign And Steed Adventure, you will have to go through a number of various areas across the Crown Tundra. One of these areas is the Crown Shrine, located at the far northern peak of the Crown Tundra. This is where you lure the Legendary Horse Pokemon so Calyrex can try to tame it, and after it does so, you will be able to catch the two combined together as one.
Interactable Pokemon
Calyrex: Level 80
Glastrier: Level 75
Spectrier: Level 75
Items
TR11: Along Outside Wall
Max Revive: Far Left Entrance
Bottle Cap: Hidden To The Right Of Entrance