Does anyone know when Xerneas'/Yveltals Nature locks in?
I found this method for faster soft resetting on Gamefaqs, but I don't know if it works without knowing when the Nature sets in for the final time:
• Encounter Xerneas or Yveltal as normal.
• Run away using the Run option.
• Go back to the Pokemon Center
• Put all Pokemon in the PC. Take/Catch one Pokemon that can easily be KO'd in one shot at this level of the game.
• Go back to where you ran from the Legendary..
• SAVE HERE!!!
• Encounter the Legendary and use a Master Ball.
• Mash through the following 30 secondish cutscene.
• Spoiler Battle
• Do anything to get your Pokemon KO'd . This is easier using Yveltal since the Pokemon has a 120 STAB that it starts with.
• After you faint you warp to the PC and you can check your stats there.
If it locks in on first encounter, it would be extremely painful to get a good nature.