Living embodiments of blasphemy formed in the Abyss out of souls that were particularly blasphemous in life. Often sent by Demon Lords to punish those who betray them, or to turn Clerics of good deities into agents of chaos and evil. Spell resistance, DR, and some immunities.
They can merge with helpless host bodies and take them over, turning that person forever Chaotic Evil. They can touch divine spellcasters and fill them with enough doubt that there is a 20% chance that they fail any time they try to use a divine ability—forever (a curse effect). Cannot be flanked.
The Shachath Demon that appeared before Grip in Chapters 151, 160, and 169 appeared as an ever-shifting amalgam of humanoid, leonine, and angelic parts. It wielded a flaming longsword and demonstrated the ability to use Greater Teleport as a spell-like ability.
First Reference: Chapter 151
Other Notable References: Chapter 152, Chapter 160, Chapter 169, Chapter 170