The leak was reported originally on NeoGAF where a user came across something interesting while watching 343’s recent ‘A Hero Awakens’ documentary video.
Around the 3:55 mark you can see a page come into focus for just a slight second. That didn’t stop the internet from bloating it up and and realizing that it’s a page from the game’s mocap performance script.
Information extracted from the script gives out possible details of the identity of the game’s primary enemy, some new abilities for Cortana and more.
Anyone interested in reading all of that can go to the NeoGaf thread here but you have been warned of potential spoilers.