Yeshom

At rest a yeshom looks like a wide puddle of glossy black tar. It can reshape itself into any creature of man size or smaller, though every form keeps that slick, liquid black sheen.

Killing eases the yeshom's boredom and hatred, so it fights willingly. It casts spells as a mage of level 14 to 18, and these effects are always active on it: infravision, tongues, read magic, unseen servant, comprehend languages, protection from good and from normal missiles, and detection of magic, invisibility, good and evil. It also wields six curse-born gifts as a 14th-level member of the curse-gifted orders, with no need for curse-warding red metal.

On a hit, ignoring armor bonuses, it chooses between engulfing the target and harming it as a black pudding would. An engulfed victim who fails a save vs. spell is drawn into an internal pocket dimension and held in suspended animation; the yeshom instantly knows everything the victim knows and can slay it whenever it likes.

Besides magic resistance, it is immune to all energy discharges (fire, cold, lightning, magic missile), to sleep, charm, hold, death magic and poison. Holy water from a temple of a neutral good god deals 2d4 per vial. Its victims are gone for good; not even wish, resurrection or raise dead returns them.

About 1,500 years ago, aranea wizard-lords of a wizard-governed nation sought immortality, stronger shapechanging and greater spellcraft, and succeeded. Several of their best volunteered for the transformation before its cost was known. At first they kept their alignments by willpower, but the undead form slowly warped them into bitter, insane recluses who hate humanoids.

Yeshoms keep no servants or undead minions. Cruel, erratic and bored, they prolong their victims' terror, rarely travel, and treat anything entering their isolated domains as prey, especially araneas, in revenge for the failed experiment. The secretive araneas simply avoid those places and seldom warn outsiders.

Yeshoms matter little to the local ecology, but they sit on large hoards gathered from their victims.