In Tzolk'in: The Mayan Calendar - Tribes & Prophecies, each player now becomes the leader of a particular tribe, each has a special ability which only that player can use. There are 13 tribes in total to secure variety of the game (You know, 13 is a pretty spooky and magical number, right?).
The whole game is also influenced by 3 prophecies that are revealed ahead of time and fulfilled when the time is right. These prophecies give players other opportunities to score points, but also lose points if the players don't prepare themselves for the prophecy effects. Again, there are 13 prophecies in the game altogether (Woohoo 13 again!).
This expansion also has new components to allow a 5-player game version and several new buildings.