A named threat of Scarlet Cave, encountered rarely and never in numbers - real Dungeons & Dragons statistics, no auto-computed shortcuts.
Layered on top of the module's own combat AI, which still picks targets and positioning. The fight below moves through real hit-point-gated phases; every save DC and attack bonus computes from the stat block above at runtime.
A real shade fights on its own initiative for as long as it survives - not a disposable add, not a static prop.
Every round it fights beside her sharpens her own blade.
Its fall earns her a burst of fury - and if nothing has replaced it by the time she's desperate, she calls a second, lesser shade rather than finishing the fight alone.
CR 8 is set against Scarlet Cave's own real ambient ceiling, not auto-computed from level alone - a genuine Rogue 4 / Shadowdancer 4 build at 8 total levels.
Hit points (52) follow this project's own average-hit-dice convention, and every save/attack bonus derives from the ability scores above at runtime - nothing here is hardcoded past the phase gates themselves.
Boss-flagged (bypasses the drop-rate roll, two loot-generation passes) and gated to a single spawn - only one Nyx Hollowmere is ever up in Scarlet Cave at a time.