Surprisingly, catching Xerneas was actually a challenge. Not as much as, say, the legendary birds and dog in FR (gods I hated that playthrough SO much), nor as much as trying to get a female Eevee into a Luxury Ball, but quite a bit more than the average 'mons I've been grabbing. (Especially since I didn't think and brought an all-battle team with no False Swipe 'mons). If I'd brought Doublade instead of Pikachu like I'd originally planned, I would have had a MUCH rougher time--and that would have been tragic, considering my Xerneas is Modest with IVs of 31/18-19/28-29/31/26-27/31. On my FIRST TRY.
I swear I must have gotten the luckiest X cartridge in the world.
