A Pokemon's nature may dictate a trade-off in two of its five stats. These stats include Attack, Sp. Attack, Defense, Sp. Defense, and Speed. Of course, to capitalize on a particular 'mon's strengths, you'll want to have a nature that greatly benefits their strength. In BDSP, you can actually cultivate a special nature that can benefit your Pokémon. Here's how to get the nature you want by being able to change it to Sparkling Diamond and Sparkling Pearl.
How to Change a Pokémon's Nature in Sparkling Diamond and Sparkling Pearl
You can change a Pokémon's nature after unlock battle tower. It forces you to beat the Elite Four for the first time. You will then have to fight for quite a while at the Battle Tower.
Battle Points (BP) are required for you to then purchase Natural mints, a relatively new element in Pokemon games. These mints can be purchased for 50 BP each, so they aren't cheap either. The names of the mints are indicative of the stat that they will increase but decrease at the same time.
How to use natural mints
You feed these items to your Pokemon as you would something like a rare candy. By feeding them, their nature will change. Their stats, depending on what nature you change them to, will also change.
You can give these mints to your Pokémon at any level. If you give it to them at level 100, they will still maintain the EVs you gave them along the way. No real statistical value is lost at any time.
Other Ways to Change a Pokémon's Nature in Sparkling Diamond and Sparkling Pearl
You can still breed or farm for a specific nature in a Pokemon by applying the tried and true backup method. This can also work for a one-time Pokemon encounter like the Marquee 'mons at the Spear Pillar or the Legendaries at Ramanas Park.
Of course, with other additions to the game like Hyper Training, you can skip a lot of saves and old ways to get your ideal Pokemon. Nature Mints can give any Pokemon you choose beneficial stats, like a Jolly nature for a Garchomp.
Pokemon Shiny Diamond and Shiny Pearl are now available exclusively for the Nintendo Switch.