As a reminder, you can’t change a Pokémon’s Nature after the fact. So if you’re serious about building a Pokémon, you’ll want to choose a good Nature for them before everything else. How do you choose a Nature, some of you ask?
1. Random Chance
The old-fashioned and very unreliable way is to keep catching the Pokémon until you randomly get the Nature you want. You’ve got a 1/25 chance to get the exact Nature (the chance is higher if you settle for more Natures). If it’s a Pokémon that’s limited in number, you’ll have to soft-reset the game if you get an undesirable Nature.
2. Madam Celadon
The new-fangled and highly recommended method is to pay a visit to Madam Celadon in Celadon City’s Pokémon Center. For the princely sum of 10,000 Poké Dollars, she will offer a fortune-telling service that guarantees all Pokémon you catch until the end of the day will have a specific Nature.
Madam Celadon will ask you which color flowers to water, followed by which color flowers to thin out. The first choice will decide the increased stat, while the second choice will decide the decreased stat. Below is a table showing which color represents what stat.
Needless to say, this is an extremely convenient way to get the Nature you want, with minimal fuss. Just be mindful that the fortune applies for the whole day. So if you’re forecasted to catch Pokémon with increased Special Attack and decreased Attack, focus on catching as many Pokémon that would benefit as possible, while avoiding those that don’t benefit (like most Fighting-types).