* A legion of demons: This is the most common and perhaps most fitting, reflecting the image of a large, organized army of demons.
* A host of demons: Similar to a legion, this emphasizes the large number and powerful presence of demons.
* A pack of demons: This suggests a smaller, more chaotic group, possibly focused on mischief or mayhem.
* A coven of demons: This implies a more organized and ritualistic group, possibly led by a powerful demon.
Ultimately, the best collective noun to use depends on the specific context and the desired effect.