A Neogi slaver-mystic, cast out of its own kind mid-ritual and abandoned in the cathedral's second level, scaled six times past its size and never quite fully returned from wherever the ritual almost sent it. It fights the same way it exists: picking at range with its mind, then twice slipping almost entirely out of the world before snapping back to punish whoever stayed close.
A ranged mind-damage bolt at whoever's nearest — 3d6+4 magical damage, and a failed Will save (DC 15) rattles loose a point of Wisdom for a few rounds.
It thins and slips half out of the world: three full rounds of total damage immunity while it quietly regenerates, then Mind Rend — a psionic burst that stuns and damages everyone still close when it snaps back.
The same trick again, but harder on the way back — a bigger Mind Rend on return. This is the module's first hard invulnerability window: every other boss's defenses still let you hurt it. The Scorned simply isn't there for three rounds, twice.
Revised CR7 → CR14 after auditing Cathedral Level 2's actual ambient encounter table: the crypt's regular trash already runs up to CR12 (Shadow Fiend, Harpy), so a CR7 named boss was sitting at the bottom of its own zone's difficulty, not the top. CR14 clears that ceiling with real room. The two Phase Shift windows are still where its real survivability lives, not its hit point total — six total rounds of the fight are simply unwinnable damage, a bigger effective toughness swing than raising HP alone.
Wisdom and Charisma both sit at 16–18 to sell a mind-flayer-adjacent psion rather than a brute; Strength stays high (24) because between Lash volleys it's still a Huge melee threat, not a pure caster hiding at range.