A named threat of The Deep Forest, 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.
He rolls against his own table of effects rather than following any fixed order - a bolt, a blink into melee, a self-altering grab-bag, a wailing nova, a draining grasp - no two rounds promise the same answer.
A new option joins the table, wider and worse.
He simply rolls twice.
CR 31 is set against The Deep Forest's own real ambient ceiling, not auto-computed from level alone - a genuine Outsider 31 build at 31 total levels.
Hit points (301) 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 Xhorlaxx is ever up in The Deep Forest at a time.