A named threat of Aventhine Sewers, 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 pure fencer's carousel - each stance's effect is stripped the instant the next one takes hold, nothing carries over.
Seven stances in all, and she is never holding more than one at a time.
The carousel's last position is also its sharpest.
CR 9 is set against Aventhine Sewers's own real ambient ceiling, not auto-computed from level alone - a genuine Fighter 6 / Duelist 3 build at 9 total levels.
Hit points (75) 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 Corvinne Ashby is ever up in Aventhine Sewers at a time.