At E3 Microsoft has announced the first major expansion for Halo Wars 2 in the form of Halo Wars 2: Awakening the Nightmare.
Halo Wars 2's first major expansion will contain a new campaign, new multiplayer maps, new multiplayer leaders, and a new co-op game mode. The campaign will take place a few months after the events of Halo Wars 2. This time around you'll be playing as The Banished, the group kicked out of The Covenant for being too extreme. The game will detail The Banished's fight against The Flood in their efforts to retake The Ark from the control of Captain Cutter.
https://www.youtube.com/watch?v=R1MVKdJ8X3E
One of the other big additions to Halo Wars 2 with the expansion will be a new game mode labeled Terminus Firefight. Similar to the Firefight mode in the FPS games, in Terminus Firefight you'll be building bases and troops, with the assistance of up to two other players, in an effort to survive enemy waves. You'll have to fight against UNSC, Banished, and Flood enemies in your efforts to survive.
The two new multiplayer leader characters have also been announced and will be shown off at E3. The UNSC will get Jerome-092, the leader of the Spartan II Red Team. The Banished will instead be getting Arbiter Ripa 'Moramee, who fans of the original Halo Wars should recognize as the main antagonist from that game. The post does note that there are still two more heroes to come in future updates.
Halo Wars 2: Awakening the Nightmare will be available for the Xbox One and PC via Windows 10 Store sometime in Fall for $20. It should be noted that Awakening the Nightmare is not part of the Halo Wars 2 Season Pass and would need to be purchased even if you got that.
If you want to know more about this and other announcements happening at E3 then be sure to check out our E3 2017 Coverage Hub.