Someone asked for a summary of post-game content, so I did him one better, and took an hour or so to type out everything on my phone. I figured I?d post it here, because why not? Here goes:
?UB Missions: You?ll get a special card near your house, go to the motel on Akala and Looker will guide you from there. Some really great Pok?mon await, and the final reward is a new Legendary and 1 million pok?dollars!
?Zygarde Cell Hunting: If you?re not finished getting all 100, there are some handy guides on the Internet. Keep in mind some are only around during specific times of day.
?Catch the Tapu(s): Each Ruin houses that island?s particular Tapu. All of them are pretty good, so have fun!
?Completion Stamps: As well as beating the game, there are another 9 stamps for your Trainer Passport. These will be explained below.
?Catch ?em All: Finish filling out your Pok?dex and head to the Gamefreak office in Heahea City for a Shiny Charm. This triples the chance of shiny Pok?mon appearing. Five of nine post-game stamps are obtained this way: one for each island and one for catching ?em all.
Find the Battle Tree: After beating the main story, an area of Poni Island will open up, leading to the Battle Tree! Beware, because a tough battle with a certain trainer from Kanto awaits when you enter.
Getting a 50 win streak in the different ?Super? modes at the Battle Tree will award you with one stamp, for a total of three. To get Super Challenges unlocked, simply get a 20 win streak in the mode of your choice, be it Singles, Doubles or Multi (if you do this one, play with a friend!).
This area also grants access to most evolutionary items, as well as many Mega Stones from Kalos!
Pok?mon Snap Pok?finder: to get the last stamp, you must embrace your inner white trash and photograph every Pok?mon more than a paparazzi. Getting to Level 5 (max level) requires 100 000 1 MILLION likes total. Good luck, and enjoy the mind-deteriorating ?gameplay?!
?Finish Pok?pelago: Max out the upgrades for each area in Mohn?s pok?-paradise. You get a lot of Rainbow Beans as a reward, as lame as it is. I recommend it just to have ridiculous numbers of berries, evolution stones and the occasional free Pok?mon to wonder trade.
Oh, and Lapras is exclusive to wandering on to your island.
?QR Codes and Island Scan: Using the QR scanner feature, you can scan up to 10 codes, with one regenerating every two hours. Each gives ten points (or in some cases, 20) and getting 100 allows for an island scan. Depending on the day of the week and which island you scan on, a different Pok?mon from outside of the Alola Dex will appear to catch in the wild. (Note: these Pok?mon do not call for help, as they are not from Alola. Also, the scan feature can also be used to get shiny Pok?mon registered in the dex for completionists).
?Collect Missing Items: There are a slew of hidden items throughout the game. Notable are all 17 of Arceus? plates, a couple evolutionary items, and all the remaining TMs (there are 100).
?Return to the Pok?mon League: As the first champion of Alola, you can?t fight yourself, right? Well, other people can fight you. There are more than 10 different possible challengers, from old Trial Captains to some close friends and even a mysterious Dragon-type trainer?
?Explore Alola Fully: Many inaccessible areas around Poni island are now free to explore. Don?t forget to visit other areas you may have missed, like Seaward Cave!
?Collect Z-Crystals: You might notice a few types are missing from your collection of cool and slightly useless single-target moves. As it happens, there?s more!
-You can find Flynium Z behind a Machamp rock in Ten-Carat Hill.
-Icium Z is near the exit to Mount Lanakila.
-Explore the desert to find Psychium Z! Not all is as it seems, and you?ll need a pattern.
-Eevium Z is obtainable from Kagetora in the Megamart on Royal Avenue, if you don?t mind a depressing side quest involving 7 Eeveelution trainers and the passage of time.
-Aloraichium Z is easy to get, if you have an Alolan Raichu. Take it to a lady in a hut on the right side of Seafolk Village on Poni Island.
?Win the Battle Royal: After completing Master rank at the Royale Arena, you get a cool new style! As for what a style is, go talk to a balding dude name Gester. You can find him at the Recycling Plant north of Malie City.
?Battle Ya Boi
Kuzco Guzma: Go to Guzma?s house on Route 2 for a pretty cool battle.
?Battle Faba: At the Aether Foundation, Faba will give you the Dubious Disc if you beat him in battle.
?Battle Game Freak Morimoto: Beating this guy in the Game Freak office rewards you with the Oval Charm, which increases the egg find rate. Also, he will fight you again each day for extra EXP!
?Get Porygon: The Aether House on route 15 (?) has two Aether employees. One gives a free Porygon, the other one gives an Upgrade.
?Get Type-Null: Talk to Gladion at the Aether Foundation for a battle and a mythical Pok?mon!
?Get Cosmog: During the day in Moon or night in Sun, head to the Altar of your game to travel through a wormhole to a time-flipped game. Go to the Lake of your game for a Cosmog! There?s nothing else to do in this dimension, by the way.
?Get Magearna: Scan a special QR code for a Legendary Pok?mon, only after beating the game!
..now if you?re truly crazy (like me), then you can go for a Language Dex. This means getting every Pok?mon.. in every language. Good luck!
If I missed anything, tell me and I?ll add it.