Ok so Necrozma is a strong foe. Bringing along false swipe is a great idea. Next, you either want to make Necrozma paralyzed or asleep. I would recommend paralysis because it lasts permanently, so give it Thunder Wave. Changing the time or waiting for night will make Dusk Balls a great option, and bring some Time Balls incase it takes awhile. Swords Dance is what I used to move along the battle. Now that you have that, you have a small list to use.
Out of these I used Mew, but taking in accessibility, typing, and Necrozma moveset, I concluded that Absol is the best if you don't use transfer, since its the only one that you can find like this. But if you transfer, Bisharp is the best. Bisharp is immune to Prismatic Laser, and is resistant to Wring Out.