Training

Base Stats - IVs - EVs - Natures - Breeding

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

Effort Values

The really good news is that Pokémon finally has an Autolevel feature, where you can autolevel your guys to Lv. 50 or Lv. 100 for Wi-Fi battles against friends/sworn enemies. This is good because getting to Lv. 100 takes forever. The bad news is that you can't just take a Lv. 20 and throw it into competition, because it likely won't have all its Effort Values yet. (You COULD, but it'll be weaker than it should be.)

Every Pokémon in the game gives Effort points in one or more stats; between one and three in total. Every Zubat you faint, all 100 million of them, gives 1 Effort point in Speed. Every Geodude, meanwhile, gives 1 Effort point in Defence. A Pokémon can accumilate 255 Effort points in one stat, but can only have 510 Effort points in all. The math works out to 127 "bonus" points that you can effectively assign to your Pokémon by fainting only certain opponents (four Effort points is one stat point at Lv. 100). Check out a full list here.

Why is this important? Unless you're some kind of nut, you don't want your Alakazam gaining Attack EVs, because it'll never use them. Those points could be much better spent on Speed or S. Atk, at which Alakazam excels.

There is a program on your Pokétch that seems to have been designed for this- the counter. You press the button and a counter increments. That's all it does, but that's all you need for keeping track of EVs. (It resets if you change programs, so if you need to take a break, write down your progress somewhere.) So you can use it to keep track of your Zubat fainting crusade.

Relevant details:

-Protein, Iron, etc, all raise a certain stat by 10 Effort points, but they're only good for the first 100 points in that stat. So if you've got 40 S. Atk EVs already, you can take 6 Calcium. Once you're at endgame, money becomes less important, so you should have enough to buy a bunch of vitamins for your first EV trained guy.

-PokéRus doubles the amount of EV you get... and there's a 1 in like 60000 chance of getting it. (I can't remember the exact number, but it's HUGE.) Should you catch it (or trade it from someone who has it) always keep an infected Pokémon in a Box, because it won't go away, and you can infect new Pokémon with it indefinitely. Once the virus goes away, your Pokémon becomes immune and is no longer contageous, but the bonus will remain forever.

-EXP. Share shares EV too! But it doesn't split it. If your lead gets 2 Speed EV, the Pokémon with EXP. Share gets 2 Speed EV as well.

-There are items you can get to increase EV gain, that stack with PokéRus. The Macho Brace is available to people who can get all three forms of Wormadam (hope you like putting honey on trees). This lowers your Speed but doubles EV gain. There are also Power items, available in the Battle Tower after the Elite Four, that give +4 to a stat in addition to whatever you should have gotten in the first place. Combining the Speed item with a Golbat, for instance, is 4 + 2 = 6 EVs, which can then be doubled to 12 with PokéRus. Getting through the Battle Tower is tough, but worth it. (EXP. Share doesn't work with these items; only the Pokémon with the item equipped gets the bonuses. Now, switching in and out does work.)

-There are Berries that can be used to remove EV, which was one of the many bones thrown to advanced players in Emerald. However, they were only good for taking off 10 EV at a time, and growing Berries is a pain. If you like your starter/guys you were using to beat the game, it might be quicker to just breed new ones and start again. Best to transfer them from Fire Red/Leaf Green/Emerald; they're a Pokéradar catch after the Elite Four otherwise.

-Rare Candies and the Daycare (1 step = 1 EXP) are the only ways to level without gaining Effort points. Keep all your Rare Candies; if you want to get into hardcore stat breeding, you'll need roughly 20 of them (buyable at the Battle Tower for BP; try not to rely on this). At Lv. 100, you cannot gain any more EV! Not that this should be an issue; few Pokémon have any reason to go over Lv. 50 these days, but it's worth noting.

-Don't give a crap about any of this and just want to throw caution to the wind? That's fine, of course. You can check to see if you've gotten all the EV you can have by going to Sunyshore City (that's the way eastern city on the main continent that you can't get to for most of the game) and talking to the Effort Ribbon lady in the bazaar. She'll give you a (wait for it) Effort Ribbon if you've gotten all your EV.

Once you've got the Effort Ribbon, the only reason left to level is to gain new attacks. Then, you can autolevel to 100 in battles, and it'll be just like you were grinding for hours. Note that local wireless battling does not have the autolevel feature, so if you want a 4 player match, everyone will want similarly leveled Pokémon.