My homebrew world was specifically designed around high-power characters and creatures. There are several NPCs in the world who are at or above 40th level, so that alters the power scale of the rulers of the planes appropriately. I've never fully statted out any of my deities, but my baseline assumption for avatars (ignoring any powers gained from divine ranks that are or are not installed in the avatars as opposed to the deities themselves) is that Demideities have 30 class levels, Lesser have 50, Intermediate have 70, and the three Greater deities each have 90. The actual deities themselves would be assumed to have at least 4 times the amount of HD/levels put into their avatars. Gods frequently put on personal appearances in my game; PCs in my epic party have actually met 8 in person including all three Greater deities.
Similarly, demon/devil lords are assumed to be extremely powerful entities in their home planes, such that the stats given in BoVD (which I will likely be using soon in the case of Demogorgon at least) are assumed to be the lowest avatars of those beings. CR 10 "aspects" would be eaten for breakfast with sides of bacon in my world, so they're clearly absurd to even think about using; the least powerful form any such being will ever present is the CR 20-30-odd version one can find in BoVD or Demonomicon articles.
I have an entire logical progression for such beings, including Overgods and how they exist, built up in my mind, though much of it has never been put to paper or text file before. To avoid boring people who don't care, I'll enclose an explanation of my quasi-scientific reasoning behind all this in a spoiler block below. Read if you dare.
[sblock]Much of this is predicated upon certain assumptions I made about what "divine" power and magic actually are, in a "real" sense, and what it means to possess and use them. I'm something of a science buff, and accordingly I created a quasi-scientific explanation for how all this works in my world.
My base assumption for this cosmos regarding magic is that it's like a fifth basic force, along the lines of gravity and electromagnetism. In real-world physics, the Standard Model requires that the particles representing the four basic forces come in three "families" each which behave differently because of differing masses (I'm greatly simplifying matters here but that's the basic gist). I decided that the "magic" force is the same way- it comes in several "flavors," each based on a particular variety of the "viton" (the name given to the "magic particle."
Briefly, the lowest, least-mass viton is the basic "life force" that gives life to beings that actually are alive; each individual viton can be thought of as a soul in its purest, most basic form. Souls create the effects they do (such as entities that are aware of themselves and their surroudings, and help mold reality) through interactions with the other particles of the universe. As beings with vitons grow and age, they accumulate more vitons now and then, which essentially glom on to the ones they started with and merge to form a greater entity that behaves as if it's one thing. This explains why "souls" as most people think of them exist, why they can retain a personality even after death, and how souls can become more powerful (such as by gaining levels). It also explains how Negative Energy has the effects it does: the negative energy is essentially made of anti-vitons, the viton antiparticle.
Basic vitons don't have a lot of uses beyond powering mortal creatures, but a few mortals learn to manipulate them anyway- this is how Monks and others who use "Ki" powers do their stuff. The next most massive form of viton is the psi-on, the psionics particle, and above that is the magion, the magic particle. Thus, psionics and magic are difficult to manipulate, but can produce more powerful effects if one succeeds at doing so. Ki powers are thus related to both psionics and magic without truly being either one, and psionics and magic work a lot like each other and yet are separate forces of a sort. Magic and psionics can manipulate each other, weakly (magic having an advantage due to being the more massive particle form), and both can manipulate basic vitons and antivitons in various ways (thus explaining all the magic dealing with life and death).
Above all these flavors of viton is the most powerful form, the Primon, or god particle. Deities manipulate and use Primons, which can (due to being even more massive and powerful than magions or psi-ons) manipulate magic and psionics to various effect, and are basically the most powerful means of manipulating or molding reality to one's will (will itself, in fact, being an effect of viton interactions with reality). Gods are assumed to be made up, in their most basic form, of patterns of self-aware Primons, which by virtue of being the most powerful form of viton can do just about anything they like to reality through manipulation of the other basic forces. Deities are, in other words, beings of pure energy that just happen to occasionally create bodies for more convenient interaction with the mortal realms.
Overgods are something else altogether- they are, as one deity told the Epic PCs directly, "as far above us as we are above you." Overgods are essentially assumed to be patterns written into the basic quantum probability waves that give rise to the entities we think of as particles and energies. They're thus more or less intrinsic to the nature of the cosmos itself, and can manipulate it in ways deities can only dream of in fevered fantasy. Interestingly, Overgods in my game are assumed to form "avatars" of their own which are actually deities themselves, meaning that while regular deities form physical bodies to interact with lower orders of being, Overgods form "bodies" of pure Primons to interact with the divine level (of course, those avatars can form physical bodies as well if they so choose- they are deities in every sense except for not being the true house of the being's consciousness).
One interesting consequence of this line of thinking is contemplating what a being made of antivitons is and can do- undead may be assumed to be "anti-souls" of the basic type, but it's fairly obvious that antivitons of the other flavors must also exist. I thus have a concept of Anti-Gods, though I've never actually sat down and worked out just what an Anti-God should be able to do and how it might interact with the rest of the cosmos.[/sblock]
