The Dread Orchestra

A legendary orchestra comprised entirely of demons. Historical accounts have described the orchestra appearing without warning to drive their audience to slaughter and then vanishing.

There is no record of the orchestra being defeated. The closest equivalent is defeat of the orchestra's Soloist: a chosen mortal bent to the whims of the orchestra, gifted with boons that make them nearly unstoppable. 

The Dread Orchestra is suspected to be the largest known continuous alliance of demons. Though membership is primarily of carnage, there is speculation that manipulation and tempus demons are included in their number.