Mr. Mime is a Pokémon with a lot of mixed reviews, due to the fact that he’s a humanoid clown that many find creepy or off-putting. However, the Galar region has its own type of Mr. Mime, a regional form which is… arguably worse, with an empty expression and batlike hair (ears? chitin?). There is good news though — this version of Mr. Mime evolves into Mr. Rime, a much friendlier-looking chap with the same psychic/ice type that Galar form Mr. Mime has. You’ll want to evolve him as soon as possible.
The first step to getting this jovial fellow is obtaining a Mr. Mime. You can do this in a few ways. The first is by catching a Mime Jr. and evolving it. Mime Jr. can be found in the Rolling Fields during snowstorms, or caught from 2-Star raids. It will evolve into Galar form Mr. Mime at level 15 as long as it knows the move mimic.
You can also find Mr. Mime itself in the game. Galarian Mr. Mime has a chance to show up near the Lake of Outrage during snowy weather. You will need the Rotom Bike to access this area. You can also catch it on Route 10 in any weather.
To evolve your Mr. Mime, just raise its level until it reaches level 42. Once it hits level 42, it will evolve into Mr. Rime. Of course, given the levels at which it spawns in the wild, it will probably be higher than level 42 when you catch it. That’s fine, just level it up once more and it will evolve.
Mr. Rime learns the move Psychic at level 48, so you will want to evolve it before then. This means you should probably catch the Route 10 Mr. Mime rather than the Lake of Outrage one if you want this move, since those tend to spawn in at a higher level than 48. Otherwise you’ll have to find the Move Reminder in any Pokémon Center.
It’s that simple — find a Galar form Mr. Mime and level it up until it evolves. Just follow these steps and you should be able to get a brand new Mr. Rime in Pokémon Sword and Pokémon Shield.