Allip

This malignant cloud of shadows boils in the air, its skeletal maw eerily babbling as the creature's claws manifest from the darkness.

Source: Pathfinder Bestiary 3.
Originally from Monster Manual 3.0
Monstrosities S&W for OSR Version

     When an individual goes insane and decides to commit suicide there is a chance they will return as an Allip. An intelligent incorporeal undead who seeks to inflict terror, confusion, and rage upon the living. The Allip will often seek revenge on those who might of played a part in it's madness. They will ignore all targets to focus revenge on the perpetrator who caused it's mental decline. An Allip is utterly insane and seeks spread psychoses on all who crosses it's path.

     The Allip uses it's babble ability to hypnotize it's victims. As their prey stands there helpless the Allip approaches them and touches their soul. While no physical harm is done their mental sanity is eroded. When all their wisdoms has been wiped away the victim falls unconscious.When it awakes it has developed a form of insanity. 

Combat: The Allip is a medium undead with the incorporeal subtype. They are a Challenge Rating 3 opponent. Since they are incorporeal creatures they do not deal physical damage. They instead deal wisdom damage.

-Babble: The Allip constantly mutters to itself. All sane creatures within 60ft must make a 15 Will Save or be fascinated for 2d4 rounds. The Allip can approach without breaking this effect. An attack by Allip will break the fascination condition.

-Madness: Anyone who makes direct contact with an Allips mind takes 1d4 points of Wisdom damage.

-Touch of Insanity: The touch of an Allip causes 1d4 points of wisdom damage if a DC 15 Wisdom save is failed. If the Allip critical on an attack it deals 1d4 points of wisdom damage plus one point of wisdom drain. (Losing Wisdom can make subsequent saving throws harder since your Willpower save is modified from Wisdom.)

-Special Defenses: Incorporeal, Undead Traits, Channel Resistance +2

     The Allip makes for a great low-level undead foe. They can be used to haunt an old sanitarium. Maybe they were mentally tortured to the point of suicide. Now they seek revenge on the torturer and all those who are associated with him. Learning the history of this tormented soul can create a grey area. Maybe the Allip in it's former life was an innocent child who was driven to suicide by external forces.

OSR Version
     The Allip is converted to an OSR Version for Sword & Wizardry Complete. This version has a couple of differences. First the babble works as a suggestion spell. Second if you lose all your wisdom you die and become an Allip is 2d6 days.

     In my last AD&D 2E game our halfling fighter was killed by an Allip and I used the OSR version. The fighter was killed once she lose all her wisdom.

• Allip: HD 4; AC 5 [14]; Atk 1 strike (no damage, 1d4 points of wisdom lost); Move (fly 6); Save 13; AL C; CL/XP 7/600; Special: drains wisdom, hypnosis.

Types of Insanity

Taken from the Pathfinder GameMastery Guide and found on the Pathfinder SRD is a quick list of possible mental impairments if your character loses all it's wisdom and you wish to make them insane.

When a creature goes insane, roll on the following table to determine what form of insanity strikes. Alternatively, you can assign the insanity to match the cause.

d%	Insanity
1–11	Amnesia
12–48	Mania/Phobia
49–68	Multiple Personality Disorder
69–78	Paranoia
79–84	Psychosis
85–100	Schizophrenia