Natures - The Basics
Natures are the Pokémon equivalent of personalities. Each Pokémon can have one of 25 different Natures, each one affecting stats differently. Natures are not directly manipulable by the player.
Like Effort Values and Individual Values, Natures serve to help make each Pokémon unique and gives you a chance to further specialize your Pokémon to fit a specific role by manipulating its stat totals.
Like Effort Values and Individual Values, Natures serve to help make each Pokémon unique and gives you a chance to further specialize your Pokémon to fit a specific role by manipulating its stat totals.
How Natures Affect Pokémon
Each Nature affects two stats. One will be increased by 10%, while the other will be decreased by 10%. Natures can give Pokémon stats that extra push at the cost of lowering another stat that they may not necessarily need.
No Nature can manipulate a Pokémon's HP stat in any way, and some Natures increase and decrease the same stat, so that in effect they are neutral Natures that don't affect any stats whatsoever.
No Nature can manipulate a Pokémon's HP stat in any way, and some Natures increase and decrease the same stat, so that in effect they are neutral Natures that don't affect any stats whatsoever.
In the above example, the Hardy nature Venusaur has very balanced stats, while the Modest nature Venusaur has a higher Special Attack than normal, and thus will be doing more damage. The Timid nature Venusaur, on the other hand, has better Speed than most other Venusaurs, and will outspeed more opponents in battle.
In general, the ideal Nature for your Pokémon depends on two things: what you want your Pokémon to specialize in, and what stat will affect your Pokémon the least if it were reduced. Venusaur, for example, does not have a very good Attack stat and typically learns move that utilize its Special Attack stat instead. Thus, the ideal Nature for Venusaur will always be one that lowers Attack. From there, you decide what you want your Pokémon to excel in. In this case, you want a Modest Venusaur for extra power or a Timid Venusaur for extra speed.
In general, the ideal Nature for your Pokémon depends on two things: what you want your Pokémon to specialize in, and what stat will affect your Pokémon the least if it were reduced. Venusaur, for example, does not have a very good Attack stat and typically learns move that utilize its Special Attack stat instead. Thus, the ideal Nature for Venusaur will always be one that lowers Attack. From there, you decide what you want your Pokémon to excel in. In this case, you want a Modest Venusaur for extra power or a Timid Venusaur for extra speed.
Manipulating Natures
Natures are determined at random when you encounter a wild Pokémon or when you hatch one. You cannot directly manipulate the Nature of the Pokémon you find in the wild, but you have a limited ability to choose your Nature when breeding.
For wild Pokémon, if your lead Pokémon has the special ability Synchronize, then the wild Pokémon has a 50% chance of having the same nature as your lead.
For breeding, the offspring will generally have a random nature from one of the different 25 available. However, if you were to give one of the parents the Everstone item, then the offspring will be guaranteed to have the same nature as the parent holding the Everstone.
For wild Pokémon, if your lead Pokémon has the special ability Synchronize, then the wild Pokémon has a 50% chance of having the same nature as your lead.
For breeding, the offspring will generally have a random nature from one of the different 25 available. However, if you were to give one of the parents the Everstone item, then the offspring will be guaranteed to have the same nature as the parent holding the Everstone.
Further Reading
Click HERE for a more in-depth explanation of Natures on Bulbapedia, covering which stats each individual Nature affects.