Training

Base Stats - IVs - EVs - Natures - Breeding

The following information is valid for the Third and Fourth generations.

Natures Table

Bonus	Penalty
	Attack	Defence	S. Atk	S. Def	Speed
Attack	Hardy	Lonely	Adamant	Naughty	Brave
Defence	Bold	Docile	Impish	Lax	Relaxed
S. Atk	Modest	Mild	Bashful	Rash	Quiet
S. Def	Calm	Gentle	Careful	Quirky	Sassy
Speed	Timid	Hasty	Jolly	Naive	Serious

Fairly straightforward. Note that a bonus and a penalty in the same stat is equivalent to having no change at all. This is good if you cannot decide on a stat you want to take a penalty in.

If you would like my opinion (...what? Shut up) the Defence and S. Def lowering natures should never be used. Very slow Pokémon, or Pokémon you plan to use with Trick Room, can make good use of the Speed reducing natures. You'll find that the most popular natures are Modest, Adamant, Timid and Jolly.

Influencing Natures

With the advent of Emerald, the Everstone gained the ability to help control natures when breeding Pokémon. By equipping it on the female Pokémon in a pairing, its nature will be passed down 50% of the time. Therefore, if you are looking for a Timid Pokémon, it makes sense to have a Timid female with the Everstone. Everstones can be found in several places in Emerald, and can be dug up from the Underground in Diamond and Pearl. If Ditto is being used in any pairing, give it the Everstone instead. Note, however, that it appears that this does not work when trying to breed Pokémon from two different languages. (As in, a Japanese and English pairing cannot use the Everstone.) If you've traded for a Japanese Pokémon, you'll have to breed it first to get an English baby of the same species, then start breeding with that. Why this is is a complete mystery.

You can also now use Synchronize Pokémon to assist with catching similarly natured Pokémon. An Abra, for example, that is Timid and has Synchronize will cause the Pokémon it encounters to be Timid as well 50% of the time. This only works in Emerald, Diamond and Pearl. In addition, you can use this trick for -standing- Legendaries in Diamond and Pearl only- it doesn't work in Emerald, for some reason. However, it does not work at all for running Legendaries.

The practical upshot of this is that you can use Synchronizers to help you catch Dittos in Emerald that have the nature you want, and if you catch several, you might find one with a good stat or two to help you get started with breeding with the Everstone.

Advanced Dittocatching

In Emerald, you'll need a Ralts with Synchronize and the nature you want to catch Dittos with. Level it to Lv. 41, WITHOUT letting it evolve. Now, use a Max Repel in the cave behind the fossil maniac's house. This will remove all the Whismur and most of the Loudred, leaving only Ditto. Now, when you encounter a Ditto, let it change into Ralts (use Growl or something) and then use a Repeat Ball. Guaranteed capture. This way, you can quickly farm Dittos with the natures you want, with good stats to get you started.