What are they and what do they do?
Having discussed Individual Values in Pokemon and how they can affect the stats of a pokemon, it’s time to go on to the second major factor in a pokemon’s development that you need to pay attention to the numbers of- the Effort Values (or EVs).
EVs are another hidden stat in Pokemon- like your pokemon’s IVs, there is no direct way in the game to get a look at what they are, but they still determine the stats of your pokemon. They are a very important factor of the game, because they affect the pokemon’s stat values, but can only be accumulated through two methods- vitamins, and battle. Before I go into that, though, I need to discuss the limitations on EVs and how exactly they affect the stats of a pokemon.
When a pokemon reaches level 100, the pokemon’s stats will be increased based on the EVs they have gathered during their training. Every 4 full EV points in a given stat will increase the pokemon’s level 100 rating in that stat by one actual point. Unfortunately, partial amounts like 3 or 2 EVs will have precisely zero effect, so precision is required if you want to train a pokemon to a particular stat number via EVs. Additionally, each stat that a pokemon has can only have a maximum of 255 EVs. It would seem to make more sense to have each stat cap out at 256 EVs, but because of the way the programming for the game works, that last number needs to be reserved for the ‘zero’ value. As you can no doubt guess, 255 is not a number evenly divisible by 4- so training a pokemon to have more than 252 EVs in a stat does precisely nothing. This does not mean you must avoid training to 255- if you’re dumping all the EVs available into only two stats, then the remaining 6 EV points can only get you a single point in something, at which point they may not actually be worth the effort after all.
This, of course, brings me to the third limitation of EVs- no one pokemon can have more than 510 EV points. Since each stat is capped at 255 and the total per pokemon is capped at 510, this means that you will have to make a rational choice about where to put the EVs you’re training into your pokemon. This can be problematic with the team that you used to progress through the story mode of the game, though, because you don’t really get to choose what pokemon the enemy trainers have. Fortunately, there are ways to fix this, but I digress. Remember that with a maximum of 255 EV points in any one stat, the most you can use EVs to increase a stat by is 63- though that’s nothing to sneeze at. On a weak stat, that’s a 50% increase- and even on a strong 300 value stat, that can be an increase of 20% or so.
With 510 EVs, you’re able to put together a whopping 127 additional stat points to put in your pokemon’s level 100 stats- and remember, since the stats a pokemon has at any given level are based on how its level compares to the maximum level of 100, that will affect your pokemon’s stats every step of the way. That’s a pretty hefty difference, and is the primary reason why you are far better off training a team at least for a protracted period of time rather than simply hatching pokemon or catching them and then using Rare Candy to make them level 100. Once a pokemon is level 100, only a few things will make the game check to see if its EVs have changed, so you’ve lost out on your chance to give your pokemon more than 100 EV points in any given stat.