Fifteen unidentified, stationary monsters sealed in the abandoned arena and considered outrageously lethal.
Carl sees fifteen red entities sitting beyond the practice-arena door through his enhanced map. No survivor has supplied a species identification because every group sent inside died.
The monsters remain quiet except for a low growl heard after Carl begins fortifying the barrier. Their inactivity may reflect sleep, containment, waiting, or a dormant quest condition.
The combination of demonic context and Astrid's Cosmic Sense suggests supernatural nature, but that classification is not confirmed. Carl considers them too dangerous to use even as a lure.
Explosives in the adjacent assassination threaten to breach the plain door, so Carl adds blast-resistant barriers and sandbags outside it.
Fifteen indistinct red-tagged shapes sleeping or waiting in total darkness behind a wooden door.
The monsters are the dormant catastrophe beside Carl's ambush site.