Stages, bosses and Extremis

Quick answer

Confirmed arenas are the ashen plains of Aqshy and an abandoned Space Hulk. The Great Unclean One is the named boss.

The store text gives two arenas and one boss name, then stops.

Aqshy is open ash. You have room for the circle until a red Ork screen or a synapse creature takes it away. An abandoned Space Hulk is corridors. A Ratling Gunner's hazard lane, or a Bloodcrusher down a straight hall, is the whole fight.

The named boss is the Great Unclean One. Extremis bosses are described as a step past a normal survivors elite. Troggoths show up in the 6 October Gloomspite reveal as the tall things behind the grots. That reads as an enemy class, not as a second named stage boss.

The art blog on 27 August promised a warzone follow-up. Until that post exists, the practical split is the one in two settings, one screen.

Official key art