Arceustar, you get Amsalp the Patrat. Since Patrat and Watchog are used often by Team Plasma as servants and disposable Pokemon, it angers your Patrat immensely. The first Patrat you see after gaining your Poke Balls must be caught, no soft resetting or any of that crap. Now, since Amsalp's family was destroyed by Ghetsis and his grunts, it scars the Patrat horribly with emotional turmoil. Because of said turmoil, it can no longer learn any moves with a BP of 80 and above. In addition, it can't learn TM or HM moves. Obviously, Alsalp is pretty messed up, so in order to heal, it must solo 40 Team Plasma Pokemon in anger for his fallen family. Whenever he sees a Patrat or Watchog, he goes into a state of shock, horrified to see his own kind working for Team Plasma. So, whenever it sees a Patrat or Watchog owned by a Plasma Grunt, it becomes determined to not end up like them, so it can't be switched out for the rest of the battle unless it wins or faints. Remembering N at the scene of its' family's destruction, it must solo N each time, barring any conflicting solos. If he can solo N all four times before the castle, he can evolve. If not, he can never evolve. In order to prove that it is finally over the turmoil that Team Plasma has put on it, it must defeat Ghetsis' Hydreigon. Have fun.~
Recap:
First Patrat you see
Can not use moves with a BP 80 or above
Can not use TMs or HMs
Solo 40 Plasma Grunts
If sees Plasma-owned Patrat/Watchog, goes into rage and can't be switched out for rest of battle
Solo N all four times before N's Castle
Defeat Ghetsis' Hydreigon
(If this is TOO HARD, I might be able to lower the difficulty a tad, if I feel like it.~ Feelin' sadistic tonight. >:3 )