[@Dawnscroll] Haven't played that game either, so I'm not the one to answer, but Xerneas goes into hibernation at the end of its life and hibernates as a tree for 1000 years. Therefore, our plan is simple - we turn him into shrubbery :P

We're also dealing with an avatar at this stage (who's nowhere near full power) rather than a full-fledged legendary, with 9-10 other avatars and hundreds of trainers in the near vicinity, so I think we're covered for the festival.