Pokemon Scarlet and Violet's DLC, The Indigo Disk, adds Duraludon and gives them a new evolution, Archaludon. Duraludon is a steel/dragon type, which makes it resistant to dragon-type attacks, which most dragon-type Pokemon are weak to. This dual type is pretty powerful and their evolution makes it even stronger, but you will need a special item to evolve them. Here's how to evolve Duraludon in Pokemon Scarlet and Violet.
Where to catch Duraludon
Duraludon can be found in the Polar Biome, primarily in the southern half. It appears pretty frequently and seems to be most common in higher-elevation areas. They aren't too difficult to find, but you can always eat a sandwich that boosts dragon-type or steel-type encounters if you are having trouble.
How to evolve Duraludon into Archaludon
To evolve Duraludon into Archaludon, you will need to give them a Metal Alloy. The Metal Alloy can be acquired in two different ways. The quickest way to get it is to purchase it from the Blueberry Academy's Student Store for 300 Blueberry Points. Blueberry Points are earned by completing various quests in the Terarium after unlocking the system by completing the first couple of story quests. The second way is to earn it as a Blueberry Pokedex reward. Once you give the Metal Alloy to Duraludon they will evolve into Archaludon.