Daemonic Creatures & Extra-Dimensional Evil
In the Marvel Universe, the word "daemon" is used to refer to evil beings of mystical origin. Daemons have greater mystical powers than normal human beings, and usually dwell upon extradimensional worlds. While most daemons are born as daemons, it is possible for a god to physically degenerate into a life-preying daemon.
Daemons usually sustain themselves by preying upon lesser creatures (generally astral forms or life essences). Daemons often attempt to prey upon the life essences of humans, and also use humans as pawns in schemes to increase their own power.
There appear to be 3 major types of daemons. The 1st type appeared on Earth before the dawn of humanity. These daemons, sometimes called the Elder Gods, were at one time closely associated with the Earth itself. The Elder Gods, most of whom were not humanoid in form, later degenerated into preying upon their own kind (since humankind had not yet been born). The Elder Goddess Gaea was the only one who did not degenerate, and she gave birth to Atum, a god who destroyed most of the elder daemons. Chthon and Set were among those who escaped the daemon-purge by fleeing Earth's dimension. Gaea infused her essence into all living things and became the goddess known as Mother Earth. (The Druid and Faerie schools of magic often invoke her name in their spells.)
Long after the departure of the elder daemons, a 2nd type of daemons arose. These daemons posses vast mystical power and dwell in (and sometimes rule) extradimensional realms. To this day, these daemons use human beings as pawns or subjects. This class of daemons includes Mephisto and Satannish. In dealing with humanity, these daemons sometimes falsely claim to be the incarnation of absolute evil, in order to exploit humanity's belief in such a being. All such claims are only elaborate deceptions. There exists a sub-class of messenger and servant daemons who serve the rulers of the daemonic realms. These beings derive from the same origin as their masters, but are of lesser power. Daemons in this category include Dagoth, Ikthalon, Sligguth and veritable hordes of lesser known creatures.
The 3rd type of daemons are also of extradimensional origin, but are nonhumanoid in form and alien in motivation. Some of these daemons have appeared on Earth at some point in their existences; others remain in their own realms and seldom deal with humanity. Daemons in this category include Shuma-Gorath, an enormous multi-tentacled slug-like creature that preyed upon humanity in pre-history, the N'Garai, a race of daemons who are the extradimensional spawn of one of the elder daemons who escaped Atum's demon-purge, and the Undying Ones, another race of daemons who originated extradimensionally.
There are also a number of extradimensional mystical beings of an evil nature whose origins are so shrouded that they cannot be classified as true daemons of any of the previous 3 types. Some are rulers of their own dimensions, like Nightmare, and may be evil gods. Some live in interdimensional space like the Dweller in Darkness, a powerful being who induces fear as a weapon. Others are simply extradimensional monsters, such as Zom, or mortals like Tiboro, Xander, Shialmar, Dormammu, or Umar.
All of the major daemons and sorcerers discussed above can grant dimensional energy for spells and all of them are linked with evil and chaotic magic (except for Gaea who is neutral). Invoking one of the evil entities is extremely dangerous, since they are merciless and regard humans as pawns at best and prey at worst. The major daemons, when in their own realms, are more than a match for all but the most powerful of sorcerers.
Heroes do not suffer a Karma penalty for destroying daemons. Regardless of their power, all true daemons are irrevocably evil and destructive and should be regarded as monsters.