Battle Factory IVs (updated 2023)

This paste is an attempt to clarify, based on my own findings, the research by JoebertIII (Smogon) and werster on IVs at the Battle Factory in Pokemon Emerald. This information is useful for anyone attempting to achieve a win streak at the Factory.

The IVs for your initial 6 rental Pokemon are:
Round 1: 3 IV
Round 2: 6 IV
Round 3: 9 IV
Round 4: 12 IV (first slot is 15 IV if you've done 15+ swaps)
Round 5: 15 IV (first slot is 21 IV if you've done 15+ swaps, second slot is also 21 if you've done 22+ swaps)
Round 6: 21 IV (first slot is 31 IV if you've done 15+ swaps, second slot 31 if 22+, third slot 31 if 29+)
Round 7: 31 IV
Round 8: 31 IV (first slot RANDOM IVs if 15+ swaps, second slot random if 22+, third slot random if 29+, fourth random if 36+, fifth random if 43+)
Round 9: RANDOM IVs (first slot 31 if 15+ swaps, second slot 31 if 22+, third slot 31 if 29+, fourth random if 36+, fifth random if 43+, sixth random if 50+)
Round 10+: 31 IV (probably)

"Random IVs" means each individual stat is randomized. All Pokemon with non-random IVs have the same IV for each stat.

The IVs for Round 10+ are listed as "probably" 31 IV because these rounds can go on infinitely, and it's possible that the same quirk appears again in some later round. It's also possible that later rounds have some other undiscovered quirk.

From a strategy standpoint, it's probably best to swap 22-28 times entering Round 8 and 29+ times entering Round 9, so that each round has at least 3 Pokemon with 31 IV. The difference in quality between a 31 IV Pokemon and most random IV Pokemon is huge. Not swapping at all puts you at a big disadvantage for Round 9 because you face Noland in battle 7 and can also face legendaries.

As for opposing Pokemon, their IVs are dependent on your recent streak at the Battle Tower. I haven't tested the exact cutoffs, but if they are the same as the opposing Pokemon in the Tower, they would likely be:
Streak of 0-6 wins: 3 IV
Streak of 7-13 wins: 6 IV
Streak of 14-20 wins: 9 IV
Streak of 21-27 wins: 12 IV
Streak of 28-34 wins: 15 IV
Streak of 35-41 wins: 18 IV
Streak of 42-48 wins: 21 IV
Streak of 49+ wins: 31 IV

There are a few exceptions to the above numbers:
- Noland 1 has 15 IV (this is battle 21 for the Silver Symbol)
- Noland 2 has 31 IV (this is battle 42 for the Gold Symbol and battles 63, 84, 105, etc.)
- All other 7th trainer battles have IVs that are one tier higher (so if your Tower streak is 0, they are 6 instead of 3; if your Tower streak is 45, they are 31 instead of 21)

You should always enter the Factory with a Tower streak of 0-6 wins, as even the slightest increase in opponent IVs makes each round noticeably tougher.