Does Trainer pokemon have natures/EVs?

Question

Like Gym leaders, Elite 4...

Answer 1

They will have natures and IVs because that's an integral part of the Pokemon data. The IVs are probably mediocre to avoid the game being too difficult.

However, Joey's Rattata in HG/SS and earlier games is specifically programmed to have near-perfect IVs. Hence he always says it's in "the top percentage of Rattatas".

Most of the regular trainers don't have EVs though, they act like "just caught" pokemon. I believe some of the more difficult trainers like the Elite Four do have some EVs to make it more difficult. And by that time in the game all your Pokemon should have naturally acquired all their EVs.

Comments

Cynthia's Garchomp has perfect IVs and EVs. Explains why it is one of the most powerful Pokemon I have faced in the games.

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Cynthia's Garchomp has 30 IVs and 0 EVs in every stat, according to this spreadsheet: https://www.speedrun.com/pkmnplat/guide/8pivp

Answer 2

Most regular trainers have 0 IVs in every stat. The more important trainers, like gym leaders, antagonists, and Elite 4, usually have higher IVs. Every Pokemon in gen 3 onwards has a nature, but the trainers' natures all seem to be completely random. I have seen no evidence that stronger trainers' Pokemon have better natures. Also trainers that you battle multiple times, like rivals, sometimes have different natures on the same Pokemon in different battles.

Gen 5 is the first generation where trainers sometimes have more than 0 EVs.

source: clicking different Pokemon games on this page, clicking either "guides" or "resources", and looking for trainer data

Comments

This answer isn't wholly accurate.

For example, in emerald, all trainers' pokemon are assigned a "difficulty byte" between 0 and 255. Most trainers have difficulty 0, but some of them (like wally) have a difficulty of 100,  and others  (like gym leaders, elite 4 members, and wally's gardevoir) have a difficulty of 255. This is used to calculate whether the trainer uses a move based on the AI or at random.

It's also used to assign EVs. Trainers have EVs and IVs set to the difficulty byte ÷ 10. So gym leaders have 25 evs and 25 ivs in every stat.

If you check the stats in the spreadsheet you linked with an IV calculator (like this one: https://www.serebii.net/games/iv-calc.shtml) you can confirm this. For example, glacia's glalie

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Which games are you talking about?

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All of gen 3 uses the system I'm describing. firered, leafgreen, ruby, sapphire and emerald all have trainers with this system - with 0 to 25 EVs in all stats, and 0 to 25 IVs in all stats (depending on their difficulty). I assume gen 4 is on the same system too, but I'm no expert on that gen.