Leaks.
http://pastebin.com/CD1uzs4M is the list of new Pokemon in order of their National Dex appearances.
Alola Forms do not get new placements in the Pokedex. Oricorio gets 4 Pokedex slots, and Lycanroc gets 2. Think of it like Nidoran from Gen 1.
Throughout the game, you will fight against 5 different Ultra Beasts. There are 8 in total. 2-4 are game-dependent.
Alola Doduo and Alola Ekans can be found after you have gotten the National Pokedex. You will also be able to take the SS Anne during postgame, but it's just a round trip, acting like the Battle Chateau. No Battle Frontier.
You can transfer Pokemon GO Pokemon to Sun and Moon. This is how you can get the original forms without transferring. Their level is dependent on its CP.
During post game, there are several trainers from past games taking vacations in Alola that you can battle. Brock, Misty, Lt Surge, Giovanni, Blue, Lance, Steven Stone, Cynthia, Looker, and Serena.
Ash, Jessie and James appear in the game as characters you can meet and battle. You need Ash-Greninja for it. Beating all three wins you Ash's Pikachu, who can change hats in the PC.
You can unlock special remixes from the past 6 games if you transfer a Pokemon from that region. It can be played using a Rotom app.
Marshadow's typing is Null, which is immune to all attacks. Its ability is Lost Soul, which, when an attack is used, takes the typing of the Pokemon who used it.
Spidozoa has the ability Prey Catch, which will allow it to steal stat changes.
