Disclaimer: The following is not to knock or judge any religious or spiritual beliefs, the terminology used is of my own and if it differs from your own, use your head, you know what I mean.
As a practitioner of Zen I have a firm belief in the power and importance of balance in all facets of life, especially spiritual. This isn't an easy achievement, for some more than others, and from this many problems and much tension are likely to arise. Darkness and Light exist not as opposites but rather as corresponding parts of a full spectrum. Neither are "good" or "evil" as these are attributes of the self, which Light and Dark go far beyond, as do the beings of each. To begin, I think it may be best to start with the basics.
Darkness, as those who know the energy of it, can feel empowering and intoxicating to a great degree, depending upon the amount. It moves in an almost endothermic manner, taking in to the self. Consumption. Decay. Chaos. This is often the nature of the Dark, and to understand the nature of the energy itself leads to an understanding to the beings and individuals dependent upon it, without balance, that is. Many are capable of casting their self aside and avoiding the selfish or "evil" tendencies that may result. That said, there are still those who have not and belong to an extreme of Darkness, which brings me to demons.
The first person to say "daemon" gets shaken for not reading the disclaimer(only joking). I say this because some are under the belief that they are supposed to be the same or that demons come from a bastardization of the word. For those who haven't done the research, there is no connection between the two besides the etymology of the word "demon", only used as a DISTINCTION, not "Christian slander", seeing as it was a Hebrew translation that started the word, but I digress.
Demons are spirits of the Darker extreme, with barely any discernable Light present. Their origins are up for debate but in working with or against them is irrelevant. Like any spirit they vary by power or "rank". Some run with the pact, others fly solo. They may have less than friendly intentions depending on their feelings towards the individual but due to the Darkness they are apart of, they generally look out for number one. That said, there are demons who will help if there's something in it for them and even those who have rose above the negative aspects of Darkness and have no desire or "self" to be served. However, these tend to be a bit harder to find and are generally neutral. Demons can be sorted in a hierarchy-type classification. At the "bottom" there are what some call "personal demons", to mean the opposite of one's guide or guardian. These operate almost entirely on a mental level of their target or "host", usually in families of those with potential to be gifted. Their objective usually revolves around the neutralizing of said potential in an attempt to block progress of one's spiritual path, utilizing fears and weaknesses and turning strength against itself in a series of complex manipulations and seeds of doubt, often leaving the target believing there never was anything but their own mind turning on itself.
Above this level are your garden variety demon. These may or may not even dwell among humans depending on their desires. Those who do target man will work on the same mental level while adding on a degree of physical and spiritual interactions. These are the kind that may use the living as energy sources, usually targeting the gifted for their higher energy outputs and control. The output provides more energy to be had, as the better control can be used to their advantage in their game. As they are of an extreme of Darkness, they require Darker energy to grow and sustain their power. To this end, they use similar tactics to first bring them down, and then offer "support", gaining their trust and more. When a medium level demon is among it's chosen target, the first sign is often a marked increase in psychic and spiritual activity, even in those whose abilities were still dormant. As the seeds of doubt are planted through subtle manipulation, other signs will start to crop up such as seeing shadows out shot, feelings of paranoia, random thoughts of doubt(of ones self and/or beliefs), objects being moved and animal disturbances. As their play progresses, they will assert themselves, or Darkness in general, to be their only ally. If this is successful, the host will feel compelled to dwell in Darkness and produce it as the demon makes offerings of this energy to make the host feel empowered by it. These tactics can be so complicated even those completely aware of their intent still fall to them while others won't even know there is a demon or that they're being used. Here, I should note, the dwelling and use of Darkness itself is not a bad thing as I have said, but in their game it is what they want from their host and this will allow them to seep in more. For those who are advanced practitioners of the Dark, they can see through this and choose to hold back any energy or donate some as they see fit. Again, all up to the individuals involved. But they choose those weaker and less likely to recognize this so they may bargain their position in an exchange more aggressively to their side.
However, as you go up the latter you'll find more powerful demons who can rise against the tide, so to speak, and can be less selfish as previously mentioned. Conversely, This is also where you'll find those with selfish desires who will go after the bigger threats and the harder targets. The difference in tactics against a target here is the capability to have a fair trade with those gifted with Dark energy as well as the desire to try to stop or turn those of the Light.
Finally, at the top of the demonic end of the Dark, you'll find the lieutenants and their leaders who run the operations and decide how to best deal with threats and work assets. Not much can be said of them past this other than they are quite powerful and will seldom, if ever, deal with the likes of mortals unless need be.
But not all spirits of Darkness are demons. At the very core of Darkness, at its collective and source, is a more powerful and universal force that likewise corresponds to the same of the Light. The force of which I speak is Death. It is not merely of biological decay, but of the singularity, the core of it all. To clarify and expand my meaning with a simple metaphor. See, as you may know, where our understanding of the Beginning ends is the Singularity from which the Big Banged. A similar singularity is found in black/white holes. See on one end we have the black hole, a force of extreme pull, sending matter and energy into the singularity. On the other end, An extreme output of pure energy with an equally gigantic push. Nothing can be created from nothing, yet in the beginning this single point DID, and created it all. This creation was Life, and as it flows it does so into Death, the two forever feeding each other. And this singularity between it all, connecting and separating the two, is naught and infinite as one.
Moving on from these philosophical matters and what have you, I shall move onto the Death energy and spirits. Death energy, or essence, can be felt as a disturbance in Life force, for obvious reasons. The first I've ever felt of it was the night before Japan was hit with the earthquake/tsunami, as it was by many others. The energy itself brings a feeling dread and can be almost painful to wield. The practice of it will often yield a proclivity to communication with spirits of the dead and Death, though some seek it's power in an attempt to create curses. But Death force itself is far beyond good and evil, it is the practitioner that makes the decision of what they want to try to do with it.
Messengers of Death are pure forms of Death. They have been seen in almost every culture and have always been neutral. The appearance of one seldom means the death of the individual or anyone they know. They usually appear to those who will soon experience a change or one who the Messenger has a vested interest in. They can be helpful with communication and the pursuit of information or work as a guide for ones path, helping them find or learn to utilize Death. There are some rare less friendly Death spirits such as Shades who can drain energy to an extreme degree, but only to anyone trying to misuse or control Death. The term shade is also used in old Greek necromancy to mean any old spirit really, but again, it's all words.
If we truly seek peace and truth we must understand and wield both Light and Dark and fear neither. It is our self that we must overcome in these practices and I do hope this has helped shed some Light on certain matters of Darkness. I hold both to be equally sacred and believe they together are the keys to the truth. Light and Dark, Life and Death, in the end it will all return to the same point in which it came.
I shall now discuss the flip side of the coin; The Light. Before I get into detail I want to discuss an important piece surprisingly misunderstood by most, the relation of religion and spiritual practice.
Religion can be a touchy subject for even the closest of friends. The reason for this is the amount of ignorance and misunderstandings of beliefs, practices or, the most common, history of what ever religion. And often, no matter how well things can be explained to either side, the biggest problem is that the arguments turn more into a pissing contest over who is more "right" than the actual truth. So, moving that crap aside, I wish to share with you the truth few can see past this haze, that religion and spirituality are in fact one and the same.
In any belief system there are founders and leaders and writers that set the terminology, rules and values, however, these are the human aspects, the parts that make the difference between each. So if we want to look beyond that we have to look at the "higher" aspects of each. The forces and sources of the information they receive: The Light. In Abrahamic religions they believed it to be their lord and his messengers passing it down to prophets through Revelation. Head East and you'll see it called "Nirvana" for the bodhisattvas or similar divine spirits and messengers. Now look across the word of religious/spiritual beliefs and you'll find Awakenings, Channelings, Higher Selves, The Truth, The Force and boat load more terms, all breaking down in the same way: Divine communication, a beautiful and powerful Light, and spirits and Messengers of the same, teaching selflessness, love and the way to the Light. The only difference is the names and where the people involved in the construction of the belief system went with it all in accordance with the traditions of the time. But these occurrences are no coincidence, and the words are just words. What stories were told and who did or did not do what ever is all up to the listener to believe or dismiss, are of no import to the big picture. Prayer, mediation, chanting and rituals all activate and focus on the same brain waves and lower functions involved in psychic and spiritual phenomenon. It's all what works best to the individual.
In all, it's the same words in different languages getting lost in translation from petty fights and our natural urge to boost our egos. But as I said, this Light is far greater than our "selves" and like Darkness, its power and will goes beyond "good" and "evil".
Light energy being the corresponding half to Darkness is naturally out-putting, hence the image of goodness and all that. But as demons can rise, angels can too fall. Like anything in magic, it's all on the individuals response and will that determines alignment. And so, in uniform of my last thread, I shall start at the bottom of the latter of spirits, working up to the force/collective aspect.
Guardian Angels, Guides and totems are a very common, wide-spread belief. Some say every soul is born with one assigned, while others believe the designation is decided by the powers that be based on need, potential and other factors. The goal of the guardian is to protect on an emotional and spiritual level, offering support in what ever way is needed while helping show the way to one's path, encouraging confidence, discipline and stability through balance. Like their demonic counterparts, they work majorly by mental processes and only with their charge.
Next up we have your basic angels who tend to visit those with more experience and progress in their path. These may or may not offer support in the same way as guardians but operate in a more spiritual aspect. These Angels will guide the way in a more direct way. Their presence can be sensed as a feeling of comfort and joy, naturally, due to the higher levels of Light. They can plant bits of information at first to grab your attention and work up to a telepathic sort of communication. They are also more capable of keeping off and clearing out Dark spirits and negative energy for their charge until they can do it themselves.
Higher up the celestial chain of command you have the upper management types who organize, watch and make plans and hold more information and power on each sprung of the ladder. The names of the ranks and duties are often speculated but the truth is that its hard to really know as they deal with higher agendas then us mortal coils. However, the more advanced the practitioner is, the higher up the chain they can communicate and deal with. Those who have seen these were held in high regard in their cultures and held equally awesome power through the Light.
This brings me to the final aspect, The Light itself: Life. The greatest of practitioners of Light sought the source and found it to one degree or another after years of devotion and discipline, though for some it is easier than others. I for instance started my initial connection with it when I was fifteen, a freshman in high school, as it took care of the demon I was dealing with like nothing. Light was all I could see and feel, as though it were radiating from me, which in a way it was. The demon had attached itself to me quite deep, explaining why it was never seen after it met the Light. To describe it as pure joy or love fails to describe a fraction of its brilliance. The feeling was only matched by the sensation of power and knowledge I could feel flow through me as I connected but even then I knew this was only the surface of it. I then opened my eyes and saw clear through my door as though it were made of glass before clenching my eyes tight and snapping out of it. Since then it and the messengers of the Light have guided me along my way, helping me connect to it more and more. The more one works with it the stronger the grasp of its power becomes resulting in precognition, clairvoyance into the souls and fates of others, and a deal more abilities as one progresses such as directly charging objects with Light energy and taking on Dark beings.
No matter how powerful in anyway either side is, they are both still halves of the whole. For one to truly be a Master they must know both Life and Death to the extreme. Both of these can't be taught or even truly explained. There's only practice and experience to learn from, which even the greatest of teachers can substitute.