Answer
- Pokemon bred in Ultra Sun and Ultra Moon are able to remember Egg Moves in the opposite version.
- Pokemon bred in Sun and Moon are able to remember Egg Moves in Ultra Sun and Ultra Moon.
- Pokemon bred in Sun and Moon are almost certainly able to remember Egg Moves in the opposite version.
Setup
If you’re interested in my process, this is where I get into the actual experiments.
There’s a few different combinations of trading that I thought could affect the way the games read Egg Moves. Because of this, I came up with four separate tests:
- Trade Ultra Sun to Ultra Moon
- Trade Ultra Sun to Sun
- Trade Sun to Ultra Sun
- Trade Sun to Moon
These four should account for all variations between the games, thanks to each version interacting with the others in some way.
The Pokemon I decided to use was Slowpoke with Stomp, an Egg Move it can inherit from the Rhyhorn family. These Pokemon were somewhat arbitrary – this test will work with any breeding pair. If you’d like to replicate the exact process I used, you’ll need a Rhydon with Stomp and a random Slowpoke of the opposite gender.
Experiment One
The first thing I did was breed the Slowpoke and Rhydon in Ultra Sun, hatching a Slowpoke with Stomp.
This is a photo of the Slowpoke sent to Ultra Moon (“UM Trade”) immediately after hatching it in Ultra Sun. As seen, it has inherited Stomp from Rhydon.
This is a photo of the Slowpoke after using the Move Deleter to remove Stomp. After this, the Slowpoke was traded to Ultra Moon…
And taken to the Move Reminder…
Success! We can confirm that Pokemon bred in Ultra Sun and Ultra Moon will be able to remember Egg Moves in the opposite version.
Experiment Two
Just like Experiment One, this test begins with hatching a Stomp Slowpoke in Ultra Sun. S Trade, pictured below, will be going to Pokemon Sun – but otherwise, this test is the same.
And just like that, we can prove that Pokemon bred in Ultra Sun and Ultra Moon will be able to remember Egg Moves in Sun and Moon.
Experiment Three
In this experiment, we start the breeding process in Sun. Here we breed another Slowpoke with Stomp so we can trade it to Ultra Sun – named, of course, US Trade.
Expectedly, we can prove that Pokemon bred in Sun and Moon are able to remember Egg Moves in Ultra Sun and Ultra Moon.
Experiment Four
We breed another Slowpoke in Sun, name it M Trade, prove it has Stomp, delete it, and send it on its merry way.
…or we would, if my Moon cartridge had gotten to that point. Unfortunately, because I don’t have a Moon file up to the Move Reminder, I can’t conclusively prove that a Pokemon bred in Sun will remember Egg Moves in Moon, or vice versa. However, judging by the previous three experiments, I have no reason to believe the answer would be different.
Conclusion
These tests are easy to replicate, if a bit tedious. I'm happy to answer more questions about the process, but I think I covered everything. Thanks for reading!