Very large and very powerful beings of pure grim created by the Corrupted three, in an attempt to gain admiration with their fellow Dead gods. Later they made the dead gods earn their name in a surprise attack. They were created in the Darkhalls, and thus were not reflected when the Crystal of creation was shattered. Demons are obsessed with consuming Radiant energy, making them the bad guys. Even the smallest of demons can take many sorcerers to kill, although there is no way to create them, so they are essentially a dying breed.
Although they are the first and most powerful of the Grim creatures, there are also many other kinds of grim creatures varying in size and power, though all are highly dangerous and bent on consuming all radiant energy.