How a Pokémon's nature affects its stats in Sword and ShieldThe nature of your Pokémon affects their battle stats.
You might not know this, but every Pokémon you catch in Sword and Shield has a unique nature that affects their stats. There are 25 different natures total, which means there's a lot of room for variance between the creatures you catch. With that being the case, you might want to catch the same Pokémon multiple times until you get one with a nature that matches your battle style. Here's a list of all of the natures a Pokémon can have in Sword and Shield along with how those natures affect battle stats.
All Pokémon Natures
How nature affects stats
How to check your Pokémon's nature
It's possible to change a Pokémon's nature
All Pokémon Natures
Adamant
Bashful
Brave
Bold
Calm
Careful
Docile
Gentle
Hardy
Hasty
Impish
Jolly
Lax
Lonely
Mild
Modest
Naive
Naughty
Quiet
Quirky
Rash
Relaxed
Sassy
Serious
Timid
How natures affect stats
The nature of your Pokémon affec...
Source:
How a Pokémon's nature affects its stats in Sword and Shield