A named threat of Amberton, 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 blighted patch takes root at the exact spot he was standing when the fight began - not wherever he happens to be now.
The blight measured from that first patch keeps widening, indifferent to where Ardemas himself has since moved.
What the blight has claimed, he claims back in one last surge.
CR 18 is set against Amberton's own real ambient ceiling, not auto-computed from level alone - a genuine Barbarian 18 build at 18 total levels.
Hit points (195) 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 Ardemas Voll is ever up in Amberton at a time.