From the announcement:
In the first mission of the Locust expansion you’ll take command of the Uthuk Y’llan as they raid dark energy from the Deeping Wound in the wastelands of the Ru Steppes. Joining your forces are the Grotesque, a new melee unit of mutated humans possessing powerful claws that can lacerate enemy troops and drench the battlefield with their blood. The Grotesque can also shoot forth sharp bone spurs as a ranged weapon, making them one of the most versatile units on the field and a fitting opponent for the magic-wielding Greyhaven Battlemages who have come to fight for the Daqan lords. You’ll also face another new battlefield threat– the mighty, armored Ironbound automatons.
Once you’ve amassed the necessary orbs of evil energy, you can summon the Doombringer, a massive, creeping, insectlike creature that can burrow beneath obstacles and devour nearby enemy troops. You’ll need the Doombringer in your assault upon the foundry where the Daqan manufacture the Ironbound. Trenches filled with flowing lava encircle the foundry, and only the Doombringer can navigtate these trenches easily.