Demon is a debuff monitor for use in raids where you can add your own debuffs to a list (or remove existing ones!) which can monitor either your target or focus target for those debuffs.
It will make sure your raid group is working effectively in order to give max raid DPS and max mitigation on the tank (if set up correctly!).
It also has the ability to count the number of debuffs on the target or focus which allows you to know when it's time to cut down on some of the weaker debuffs that are up.
*This version also includes an update by nemes for spellIDs so credits to him for that one