Not really sure if this belongs here, in Creative Projects, or in Other Games. It's basically just an idea I've been tooling around with for a while to "explain" the existence of demons in some fantasy setting or another, and also grants guidelines for how to flesh out a large menagerie of the beasties.
So here's how it works. In essence, demons are the darker side of humanity, embodying all of the dark and selfish feelings that humans possess and/or experience. For the sake of simplicity (and also for throwing in a biblical reference in a game, which is a HIGHLY original and clever idea), we'll use the Seven Deadly Sins as a guideline for determining what a "dark thought" is. This is just for making an example, a working product of course does not need to confine itself to such old ideals.
A peasant man is once again bothered by his overly-talkative neighbour while trying to work. He experiences a twinge of annoyance and frustration at having to deal with this loudmouth again, and a scowl passes over his face as he attempts to keep working while ignoring the intrusion.
In whatever parallel dimension happens to be home to demonkind, a minor demon of the sin "Rage" (also "Wrath", depending on translation and taste) is spawned into pseudo-existence. We'll call it an "imp", just to give everyone a rough picture of its petty maliciousness and overall lack of strength.
Since such thoughts are unfathomably common in normal human minds, there are thousands of the little buggers crawling around. But each individual one is limited by the passing nature and overall pettiness of the thought that created it, and as such they are all rather weak and unremarkable. They make up for it in numbers, of course, and act out what is essentially the physical representation of "the straw that broke the camel's back", as everyone knows that it sometimes only takes one more minor annoyance in a long string in order to make someone snap.
On to the next example, we see a cultured gentleman observe his rival, who has always been at least two steps ahead of him. Born of higher blood, endowed with greater wealth, blessed with an irresistibly charismatic nature and dashing good looks, he is utterly loathed by the aforementioned gentleman for his good fortune. Even the beautiful lady that the gentleman's heart longed for seems to have taken a liking to the rival.
The perpetual lower status without hope of redemption, combined with the emotional dagger of a broken heart, spawn a seething and all-consuming concept of jealousy in the gentleman's mind.
In the depths of the other dimension, a greater demon of Envy is created. This creature is incredibly powerful, as it was created not only by the stronger nature of the emotion, but also by the more powerful nature of the gentleman's mind in comparison to that of the peasant (a philosophical mind is more capable of grasping stronger and deeper concepts of the various emotions than that of a commoner, although it may be harder to move it to such emotions than a simpler mind). The result is a dangerously powerful and influential being.
That's the basic setting. That allows you to cook up a more involved backstory explaining the existence of demons (or simply leave it as it is), and also define numerous different "levels" of the different emotions, thus creating a great number of varied demons to populate your world (or netherworld).
To expand on this idea, we enter into the relations between demons and humans, and begin defining reasons for "a deal with the devil".
This is something that came to me just recently, so it's not all that thought-out yet. However, one reason for demons to seek interaction with humans is to encourage and nurture the various emotions that created them. They would constantly attempt to access the human world in order to cause events that would make humans feel more and stronger emotions of their kind.
Bargains enter the picture when someone feels so driven by a particular feeling that they contact demonic entities in order to sate it. A demon of the corresponding type shoulders his way to the front and offers the human succor in exchange for a partnership of sorts. A contract, if you will.
What this does is bind the human and the demon together. The demon will be forced (by his own interests, not by any writing on a scrap of paper) to fulfill the human's wish and do whatever it is that the human is feeling so strongly about. This could be opening the way to murder a hated opponent, or granting greater the human with greater wealth and power than his competitor.
However, this only serves the human, not the demon. The demon gets its part by influencing the human's life so that he encounters another, perhaps even greater circumstance which creates its own, stronger feeling of whatever sin the demon represents.
Due to the bargain, this thought is channeled directly into the already-existing demon rather than spawning a new one. This makes the demon stronger and more influential, allowing it to take even more control over the human's life (among other things). The human will continue to invoke the bargain in order to help him against whatever latest peeve has taken hold of him, and the demon will continue to set new problems in the human's path. The human will eventually be reduced to madness or death by the all-consuming nature of his emotion. The demon, meanwhile, will have grown considerably stronger by feeding off of the pact.
I happen to find this a very intriguing idea for explaining the origin and behaviour of demons. It does have a few rough spots, however. For example, how would one represent a demon of Sloth? Furthermore, what would a pact with such a demon entail, and why would anyone enter into one?
Human: "Uggh, I'm so tired... I'd do anything to get a couple minutes of sleep..."
Demon: "Weary? Look no further! Just sign on the dotted line. In blood, preferably"
Human: "Zzzz... Wow, that was refreshing!"
15 minutes later...
Human: "Damn, I'm starting to get pretty sleepy"
Demon: "Somebody say my name?"
Any comments on this? I just happen to really like a demonic element in games, but one thing that has always bothered me is a fantastical element without an explanation. I've always liked things that have a reason for being there, whereas inexplicable teleportation/demons/mutants/elves have always been a source of irritation for me...