Allips were the incorporeal remnants of persons driven to insanity who then killed themselves. They were a type of undead creature commonly conjured by evil spellcasters using the more advanced versions of the summon undead spell.
Allips were spectral variations of the persons they once were, with nightmarish, warped features befitting of the madness that possessed them. Their lower portions trailed away into a dark fog as they floated.
An allip had the ability to drain sanity from any creature it touched, growing more powerful in the process.
An allip was as insane in death as in life; anyone detecting an allip's thoughts by magic or telepathy was driven to the same madness.
An allip's only desire was revenge on those who supposedly pushed it over the edge to suicide. They swung wildly at any creature they detected, unaware that their incorporeal forms could cause no physical harm. They babbled constantly in incoherent whines. This mad muttering could hypnotize any sane creatures within a 60-foot radius.