A named threat of North Goblin Coast, 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.
The nearest fallen thing that isn't a person gets eaten - and every meal leaves a permanent shell of bone behind, up to five.
One meal further than the rest sharpens more than just his hide.
He fights exactly as hard as what he's already swallowed.
CR 20 is set against North Goblin Coast's own real ambient ceiling, not auto-computed from level alone - a genuine Giant 10 / Barbarian 10 build at 20 total levels.
Hit points (260) 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 Gnashjaw is ever up in North Goblin Coast at a time.