Natures are a Pokémon individuality that constitutively impacts the outgrowth of a Pokémon's stats.
A Pokémon's Nature and its affected stats are highlighted on the hover-over Pokémon card; see the pictorial illustration to the right.
Natures affect the statistical outgrowth of two non-HP stats: one additive stat that it increases and one subtractive stat that it decreases, thereby affecting the Pokémon's stats bilaterally. The differential produced by Natures is 10% of the raw stats.
There are also five neutral Natures that are completely impactless on the Pokémon's stats and are considered fodder for Pokémon that are to be unaffected by Natures; read the tabular index below.
They are hereditarily determined upon the Pokémon's obtention, and they are not changeable for most Pokémon after they are determined; they are static and thus the Pokémon can only have its initialized Nature for its entire existence. The only caveats are Legendary Pokémon, due to their obtainability's discontinuities; for a price of 75 PvP Coins, you can purchase a Nature Reroll Ticket from any PvP Master for 75 PvP Coins apiece to randomize your Pokémon's Nature anew.
While the determination of Natures are randomized, the Synchronize ability can be employed to enhance the chance of inheriting a desired Nature on wild Pokémon. If a Synchronize-possessor is used as the lead Pokémon and has not fainted, the wild Pokémon has a 50% chance of inheriting the same Nature as the possessor; this is the most facilitative mechanism used for obtaining the desired Nature, which is a sheerly adventitious hunt, otherwise.
List of Natures
|Additive stat (+)||Nature||Subtractive stat (-)|
|Special Defense||Careful||Special Attack|
|Special Attack||Rash||Special Defense|
Determining your Pokémon's optimal Nature
Akin enough to determining the optimal EV apportionment for Pokémon and what acceptable permutations of IVs that there may be, the crux of the conundrum is knowing what stats are the most vital to your Pokémon.
A tapestry of factors must be considered to determine the optimal Nature of a Pokémon, which include: the Pokémon's Base Stats (higher base stats greaten the differential of the Natures itself), the most viable moveset of the Pokémon for the offensive statistics, extrapolated PvP match-ups, the Pokémon's archetypal role in battle, and so forth. For example, Steelix's putatively optimal Nature is Impish, which increases a Pokémon's Defense and decreases its Special Attack; this is attributable to the Pokémon's tremendous Defense Base Stats and the predominance of Physical-powered moves in its move pools.
Due to various complicators, such as the unpredictability of PvP match-ups and considering whether or not the Nature is compensating for IV deficiencies in the stats, for examples, there is not any categorical guideline for determining what is the optimal Nature for a Pokémon; there are only a set of factors that you must consider to determine it at your own discretion, as noted above.