Pokemon Sword and Shield are full of strange and wonderful monsters to collect, but some of them – especially Galarian Yamask – are more of a pain than others to train and evolve. Yamask is one of Sword and Shield's Galar forms, which take existing Pokemon and put a new, regional spin on their designs.
The concept of regional forms was first introduced with Pokemon Sun and Moon's Alolan forms, based on the idea that Pokemon who had moved to the Alola region's islands would have evolved differently than their mainland counterparts. Pokemon Sword and Shield continue this idea, expanding regional Pokemon forms beyond Generation I Pokemon. Several of the Galar forms, like Meowth and Zigzagoon, received entirely new evolutions, replacing Persian with Perrserker and adding Obstagoon after Galarian Linoone. Galarian Yamask is one of these Pokemon, and – like evolving Galarian Farfetch'd into Sirfetch'd – it requires some extra work to get to see its brand new evolution.
Instead of evolving into a Galarian form of Cofagrigus, Yamask's normal successor, Galarian Yamask evolves into Runerigus, a mess of stone tablets held together by ghostly energy. Luckily for players who don't yet have a Galarian Yamask, it's not one of Pokemon Sword or Shield's version-exclusive Pokemon. Player can find a Yamask fairly easily in the overworld on Route 6, accessible after beating either game's third gym. After getting one, players will need to let it get hurt pretty badly in order for it to evolve. It may seem counter-intuitive, but Galarian Yamask has to take at least 49 damage in a single move in order to activate its evolution. The easiest way to make this happen is to give Yamask a Focus Sash item and battle a powerful opponent. One Focus Sash can be obtained from a trainer in the Hammerlocke residence pictured below.
Give the Focus Sash to Yamask and take it into battle with one of the "very strong-looking" Pokemon wandering around in the Pokemon Sword and Shield's Wild Area. Most of them should be able to hit Yamask hard enough to take it out in one shot, but the Focus Sash will let it hang on with one HP. If players have already used up their one early-game Focus Sash, they won't be able to find more until reaching the Battle Tower after the main story. If that's the case, players will just have to battle enemies closer to Yamask's level. Just keep battling Pokemon until one of them damages Yamask by at least 49 HP but without knocking it out. After that, Yamask is ready for the final step.
To finish evolving Galarian Yamask, take it in its damaged state (i.e. don't heal it after it's taken 49 damage) to the Dusty Bowl zone in the Wild Area. The Dusty Bowl is located straight ahead of the Hammerlocke entrance to the Wild Area, but players will have to go down the hill to the left once after warping there to get around the steep cliff. Next, head to the large stone arch pictured above. When the player walks beneath this arch, Galarian Yamask's evolution will trigger, turning it into the terrifying Ground- and Ghost-type Runerigus.
Pokemon Sword and Shield released for the Nintendo Switch on November 15, 2019.