Guild Leagues
Your guild is assigned to a random league of 14 guilds. All guilds in the league will race each other to be the first to clear raid bosses and entire raids for each difficulty for each tier. Prizes are awarded for 1st, 2nd, and 3rd place finishes. Completing each difficulty while being in the league also awards prizes.
The GOAL of this league is to foster a community feel. As such, there will be an observer mode available where people can watch. Rival league members can make attempts and see your progress in real time. There will be a league window that displays league records and best times. You will get an option for casual or elite leagues. Casual league will be for guilds that only want to clear heroic. Elite leagues will offer improved rewards and they will given for clearing mythic raids.
Guild rosters are LOCKED when your join a league. That means any encounters cleared with toons that joined the guild after the lock will not count toward league progress. So making sure you are covered with enough alts to tank, heal and dps is recommended before locking your roster.
You cannot leave a league once you join. You can have other toons in other guilds and those toons can be in other leagues. Again, league assignment is random so you cannot fill all 14 guilds in a league.