What is Nature?
Natures are characteristics that subtly influence how a Pokémon's stats grow as it gains experience.
Let's check pokemon Mr.Mime as an example:
Each Pokémon can have a Nature that affects two of its basic stats, boosting one by 10% while decreasing another by 10%. There are 25 different Natures, with various combinations of boosts and decreases.
Some Natures have no effect on stats, boosting and decreasing the same stat. Below you can check all existing natures: