The purple legendary bird can be found in the Crown Tundra. This guide on Where To Find Crown Tundra Legendary Bird Articuno In Sword & Shield will tell you where you need to go in order to track down this rare purple legendary bird Pokemon in the new area introduced with the DLC.
The bird you are tracking down is actually an Articuno, one of the legendary birds from the original Pokemon games. However, it’s had a bit of a makeover since then. With a new selection of moves, a brand new appearance, and a change in type, Articuno of the modern era is nothing to be trifled with.
When you approach Articuno, save the game. He will duplicate himself and if you guess wrong, he will fly off. It’s best to save there and keep trying.
Articuno Location #1
You can find Articuno here, in the Old Cemetery on the Crown Tundra map. He flies quite high in the air and then duplicates when you get close. Stay nearby and after it vanishes, it will lunge down to attack you, you can then attempt to catch it. If it doesn’t lunge at you, it will move to somewhere else and can chase it down.
Articuno Location #2
If Articuno is not in that location or you fail to catch him on your first attempt, you can also find it at the Snowslide Slope. It’s at the very top of the slope, near the cave entrance. It’s on the cliff that overlooks the entrance to the ruins below.
The legendary Pokemon in the DLC can sometimes be very difficult to get. I often used 40-50+ Ultra Balls catching each of them to this point. Before attempting to catch any legendary make sure you save the game and you’re stocked up on the highest level Pokeballs you can find.