Chinese Leak is 90% real. Some things I will guess were purposely said wrong. Some of these will also be wrong.

~118 New Pokemon
~28 Alolan Pokemon
~13 Mega Evolutions
~ 2 Post Game Islands.
~ Artificial Island is part of the main storyline and is known as Ahinauana Island.
~ The south island is called Omaomao Island and has the battle facility, post game story and an entire island to explore.
~ The northeastern Island that is seen on the map is Alani Island and has a few towns and wilds.
~ Nature Reserve will make a return and is now larger.
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~ Alolan Hypno is Dark/Poison
~ Alolan Milotic is Fairy
~ Alolan Flygon is Bug/Dragon
~ Alolan Persian is Dark/Poison
~ Alolan Snorlax is Ground/Dragon
~ Alolan Lapras is Ice/Dragon
~ Marshadow is a Wolf that is Ice/Dark
~ Ortusinus is a Dolphin that is Water/Fairy
~ Abyssal Ruins will have more story.
~ There are 5 Guardians, 1 in which is an Mythic Pokemon.
~ There are 4 additional Mythic Pokemon.
~ The snowman pokemon that is Ice/Ghost is Snoraith.
~ There is a 2 stage moose pokemon that is Grass/Steel
~ There is a reef triggerfish that is Water/Rock
~ There is a 2 stage nene Pokemon Flying/Ground
~ There is a 5th Legendary Pokemon Toriki Fire/Grass.
~ There is a 2 stage tiger shark pokemon that is Fire/Water.
~ There is a 3 stage Hibiscus Pokemon that is Fairy/Fighting.
~ Lilie will get the the starter that is stronger than your's, but will not start battling till midways in the game after Zygarde Core is stolen from her. She will ask you to help her.