Calyrex is a unique legendary in Pokémon Sword and Shield’s Crown Tundra expansion it is made up of two Pokémon. You go through a story quest to reunite Calyrex with its faithful steed, either Spectrier or Glastrier, and you have to choose between the two. The first is an Ice-type and the other is a Ghost-type. With Calyrex being a Psychic-type, the two combine to become a dual-typed Pokémon that you can use. But what the game doesn’t explain to you is that you can separate these Pokémon from one another and use them separtely.
For those interested in using two legendary Pokémon rather than one, doing this is extremely simple. Once you capture Calyrex with its faithful steed after going through the story quest, you should have it in your inventory. You will also have the key item Reigns of Unity in your inventory, which is what Calyrex uses to control its powerful horse Pokémon. You then need to have Calyrex in your Pokémon roster with a free space, use the Reigns of Unity on it, and the Pokémon breaks apart.
You should then have two Pokémon you can use. Calyrex will be a Psychic-type, Spectrier will be a Ghost-type, and Glastrier will be an Ice-type. Unfortunately, for those who only have a single copy of Pokémon Sword and Shield, you can only choose to have one copy of Calyrex with their faithful steed. If you have two copies of the game, you can have Calyrex as a Psychic and Ice-type and a version as a Psychic and Ghost-type, and you can separate both types so you now have three unique Pokémon and two Calyrex.