Two things I recently noticed on my X playthrough:
1. The berry bushes have a growing animation, which is just a sound with a few sparkles. I haven't seen any mention of it online and haven't been able to record it.
2. KOing an enemy with U-Turn(probably Volt Switch too) and leveling up prevents the level counter from incrementing. This doesn't have any actual gameplay effects, so it's just a small visual bug:
https://www.youtube.com/watch?v=H2iiXLZ6MlM