Last night during its Gamescom stream Microsoft announced some new content for Halo Wars 2 in the form of the DLC Awakening The Nightmare. This expansion will be set some months after the main campaign of Halo Wars 2, with a new a Banished campaign. The faction has gone to extreme lengths to gain any ground in the war, and in doing so awaken the flood.
Awakening The Nightmare will add new leaders to the fray as well as a new mode called Terminus Firefight. Spectator Mode and Arena inclusion is being updated to allow matches to be watched live.
Source: Xbox.com