This information comes from CoroCoro…
– You follow Entei, Suicune, and Raikou around Johto, just like in the original games. However, Eusine is stalking Suicune.
 – Ho-Oh is in the Tin Tower and Lugia is in the Whirl Islands, both at Level 45.
 – There is a new feature in the game called the “Pokeathelon,” which is a mini-game feature that uses the stylus.
 – The Pokemon Gyms have various traps.
 – Red Gyarados appears in the Lake of Rage at Level 30.
 – The Kimono Girls are part of the storyline and you meet them many times.
 – Dialga, Palkia, and Giratina each learn moves they could not previously learn – Metal Burst, Hydro Pump, and Shadow Sneak (respectively).
 – There are 9 mini-games. One of them could be the racing game I saw at the early premiere of the Arceus movie.
 – Eusine, a character from Crystal, is in the game.
 – Latios and Latias are in the games at Level 30.
 – Mewtwo is in the game – Possible Kanto confirmation if it turns out to be true.
 – Lugia and Ho-Oh have a “hidden ability.”