A named threat of Aventhine Hold - Level 2, 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 single countdown ticks on whoever he's sentenced, round after round, whether he lands a hit or not.
The count doesn't reset when its target falls or flees - it simply passes to the nearest enemy standing, unbroken.
Zero on the clock is a verdict, not a warning.
CR 18 is set against Aventhine Hold - Level 2's own real ambient ceiling, not auto-computed from level alone - a genuine Undead 18 build at 18 total levels.
Hit points (185) 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 Castellan Morrow is ever up in Aventhine Hold - Level 2 at a time.