Supernatural Beings refer to all entities which exist beyond the scope of what most people consider the ‘natural world’. It refer to entities which are both human and non-human. All supernatural creatures posses an Impulse, an overriding urge which is at the core of their nature.
The origins of Supernatural Beings are extremely varied: some are born of the actions and byproduct of human existence while others are born of pure belief and superstition. Others are primordial entities which supposedly predate humanity.
Classification are not a hard and fast rule. There are many creatures which overlap more than one category and these categories are, themselves, nothing more than arbitrary definitions created by humans.
All supernatural beings have an Impulse: it represent the call of their inner, true nature or some base physiological need. An Impulse can be resisted/kept in check or allowed to completely overwhelm the mind of the one suffering from it. Those beings who let their Impulse run free are generally stronger but more dangerous to humans. Note that an Impulse does not need to make a creature antagonistic to all humans but it always imply a certain lack of sanity or an inability to act beyond one’s nature. For example, an ‘Angel of Vengeance’ might still act completely normal toward those it is not hunting down but against those it will, the creature will act like a merciless and ruthless killer.
Supernatural Being cannot fully change what they are but, under circumstances, they can certainly transform from one type of being to another. The process is rare, usually complex and require an outside power source to ‘jump start’ the transformation. Given the existence of broken fragments of parts of the multiverse, such fragments of powers do exist, free to be tapped into. However most acquire their power through bargain with a higher power. The most famous cases involve vampire being becoming full vampires, either by being elevated by another vampire, consuming it or acquire the power of a destroyed vampire as well as Lich, which are human mages sacrificing their lives to become undead creatures and fuse with their own magic. Mortals or demi gods becoming some form of divinity, either via taking a new place in a pantheon or via some other means are also a form of ascendance. Presumably, much more exotic form and cases exist but they haven’t been recorded.
Becoming undead is by far the most common, albeit weakest, form of ascendancy and in some cases can even be seen as a descent, not ascension.
It is said that when a concept become true once, it become true forever. The concepts which compose the being are now part of the nature of reality and can, under the right circumstances, be repeated. This is how new supernatural being come into existence. These creatures posses a reflection of sorts of their progenitor, but neither its full nature nor any link to it. This also allow the existence of creatures who are similar to something else without being directly related. To use the example of vampires again, the primordial vampires reflected themselves in all the lesser vampiric beings.