From the post:
Legends of the Alliance is a free companion app for Imperial Assault that promises to revolutionize the way that you play the game. Until now, your campaign games of Imperial Assault have been divided between two sides. Up to four players became heroes of the Alliance, fighting for freedom across the galaxy. The final player took on the role of the Empire—commanding Imperial forces, triggering powerful events, and serving as the heroes’ opponent over the course of the campaign.
With the Legends of the Alliance app, you immediately have the chance to challenge and reform these existing roles. The Legends of the Alliance app assumes the role of the Imperial player—handling every aspect of the game once controlled by that player, whether commanding the Imperial forces in battle, springing traps on the Rebel heroes, and inviting you to explore secret bases and strange planets in entirely new ways.
At its core, Legends of the Alliance introduces a fully-formed, cooperative way to play Imperial Assault, controlling all of the soldiers and responsibilities once handled by the Imperial player and freeing you and your friends to unite against the Galactic Empire.