The heroes stepped through the portal opened by Axiomus the Magus. Within the halls smelled of dust that had laid dormant for centuries. Within the still halls, nothing moved. At least until our heroes came down the halls.
Within the still rooms, humanoids began to shuffle. Crystals embedded in their chests and foreheads flared to life and they started to shuffle down the still passageways towards the heroes.
When the battle had ended, the crystal soldiers laid strew about. A shadow demon had been dispatched. But not before he had told them of the horror that is the crystal soldiers. They were once men. Embedded with the crystals, they had their bodies slowly taken over by whatever malignant force controlled the crystals. Driven slowly mad as their spirits are consumed, slowly, over an eternity as a slave to the crystal and refashioned into an essentially a mechanical man.
The shadow demon suggested that they had the way to create more, and to create more was the path to the power that they sought.