Game Freak have issued a challenge to all Pokemon Sun and Moon players: Catch 100,000,000 critters before December 13. If you pitch in, there's something good in it for you.
Sun and Moon make use of a mechanic known as "global events", which are limited-time festivities where players try to meet a collective goal. Here's the official word:
If everyone combines their efforts to catch 100 million Pokemon between November 29 and December 13, 2016, each participant will receive 1,000 Festival Coins as a reward. If the goal isn't met, Trainers who contributed will still receive a participation prize of 100 Festival Coins. To be sure that your Pokemon bounty gets included in the final count, be sure to use Game Sync by December 13.
To participate, you need to head into the Festival Plaza, which is accessible by pressing X and then tapping on the Festival Plaza icon. Once there, head inside to the castle. Use the PC on the right and select "game sync". Make an account, and then talk to the lady next to the PC. She will give you the option to participate in Global Missions, but only after you do the Game Sync stuff.
From there, well, it's all up to you to catch em all, as they say. The game will keep track of how many creatures you've contributed to the tally, and you can check that number by going into the Festival Plaza and talking to the lady next to the PC once more.
While 100,000,000 may seem like a paralysingly insurmountable number to catch, remember, it's a collective thing -- so if enough people participate, it hopefully shouldn't be too difficult to achieve.
Why go through the trouble? Well, you can use Festival Coins for all sorts of things within Festival Plaza, whether it's purchasing more items, recolouring your clothes or levelling your monsters, depending on how you've developed your Plaza. One thousand coins is a lot of money to mess around with, and if you're going to be playing anyway, you might as well get something out of it, no?
Good luck! Make sure to stock up on Pokeballs.