Demons externally resemble Earth humans, with their red skin being the only visible difference. They typically have red or brownish red hair, which can turn grey with age. Their bodies show the same variance of humans, however the entire race seems to have a single ethnicity.
Some Demons can grow to be much larger and muscular than humans; Oblivion was particularly massive.
Despite the apparent similarity with humans, Demons have significan anatomical differences.
They have several redundant organs, including three hearts and six lungs. (Beyond The Impossible#109) They heal much faster than humans, have greater reflexes and superhuman strenght, with adult males able to lift several tons with ease. (Beyond The Impossible#78)
Demons age about four times slower than humans, however older Demons are significantly more physically active even in their old age.
Demons can survive much higher temperatures than humans, easily surviving on the surface of Hell even when in close proximity to lava. Their bodies require much less sleep, food and drink than humans; they typically drink hot salted water to hydrate themselves. Demons don't have navels and males don't have nipples.
Demons have almost no sex drive and consider having sex for pleasure an alien concept, conceiving children only under orders.
All Demons are born with a physical connection to the Blood, a universe-wide energy field that connects all living beings. They are able to utilize this connection to conjure physical objects made of Blood energy, typically taking the form of energy weapons. This is learned very early in life: Torn's daughters were able to create weapons before they were potty trained. Older Demons can use the Blood for telepathic communication or creation of portals for other worlds.
Religion and philosophy
Demons don't worship any god and most practice a philosophy of neutrality, believing that the universe is in a natural state of balance that should not be influenced. Others hold that, when other beings create an unbalance, it is the duty of the Demons to restore the natural order.
Demons don't use last names, with a single name being used to identify the person; occasionally the name can be extended with the name of the father or place of origin. For example, while Torn is his only name, he is sometimes addressed as "Torn, son of Reaper" or "Torn of the Seventh Circle of Hell". Similarly, his daughter Laceration can also be called "Laceration, daughter of Torn".
All Demon names are common nouns, typically translated into other languages when speaking to non-Demons.