We know of two worlds beyond our own that are full of tortured souls and the caprices of a dark god: the Abyss, honored by those in the Place-Not-Named and Vortex, sacred in the Khan's Empire. Each has its own denizens (Abyssals and, from the Vortex, Abominations) and they are a match for even the greatest mortal. Spells and sacred weapons (if any can be found) may banish them from our world again. Sages state that such creatures can not really be killed. Normal mortal weaponry may, in time, banish them but many will be slain in the attempt.
The Abyssal of Darkness
This horror appeared and sucked the life force of King Dallarus of Windamere; it nearly destroyed the entire castle. Only the determined efforts of the Barons of the Realm, the rescuers of the (then) Princess Arana, and the magic of the Thaumaterge Royale sent it back to The Abyss.
It appeared as a huge column of darkness topped with a type of head with two eyes like embers. From its body came the sounds of tortured souls and fear spread before it. When it killed the King, a second set of eyes, eyes of a darkness absolute, opened as it hugged the doomed monarch to its body and drank his life force and, perhaps, his very soul.
The thing appeared concurrently with a platoon of winged imps. They were as nasty as the thing they called "Their Master" and spoke Common as well as a hideous tongue among each other.
The Darkness did not speak, though it hissed and groaned and, finally, screamed as magic sent it back to the Abyss.
The Imps
These winged abominations invaded the castle and many fought with the acolytes of Markik, whom they targeted for death. All present perished, and only the Mendicant of Orozan the Beggar God managed to drive some of them back into their abominable home. The final Imp was found in the Royal Library, searching formulae in previously hidden books of magical lore. It took the combined efforts of several determined fighters to banish it.
The creature was a winged humanoid with glowing eyes, a lashing tongue, and razorlike claws. It likes to harry its foes when they are captive, flaying their clothing and even skin off, but not to the point of death. They pursue this form of slow torture for many hours, even days. Despite its small size, it could lift humans it clutched into the air.