...And Eternity
So at last, we reach the top of the pile, and the Demiurge and its progenitors are all the entities left to describe. Here, my pseudoscience explanations begin to fail, because beings of this level are so far beyond anything we mortals can directly deal with that mere words can surely not suffice. But, as the British say, let's have a go anyway.
Even during the full game, including the end session on January 30th of this year, the PCs never directly met the Demiurge itself- in fact, the only Eternals they did meet (if one doesn't count monsters like the Nehaschimic Dragons I threw at them, or the Neutronium Golem) were a strange old man whose true identity they never guessed (I intended him to be a Lipika- the ex-Supreme Beings who act as caretakers of the Akashic Record) and the progenitor of their own flawed Reality, who gave Its name as SEPHIROSOPHIA. The true
nature of the Demiurge was also never explained to them, other than giving them the notion that it was sort of a "Sidereal" for all of Reality itself, but of course that's not accurate either given that it's actually of a different order of being altogether.
This is at least in part because I myself never really worked out the details. I'll digress here back into the history of my musings upon beings greater than gods, and explain what little is left to tell regarding Originals as I conceived them before the IH. My conception of these beings was deeply involved with a history I had for the "Incomplete Creation" that the game was assumed to be taking place in; I wrote a backstory which today looks suspiciously Judeo-Christian (though perhaps that's not inappropriate since the game concept of Eternals is heavily influenced by the Aeons in Gnostic Christianity).
Basically, I said that there was a massive "world" which was the first creation, dubbed simply Origin, and it was made by beings called Originals who came to this corner of existence from elsewhere (in fact, only they are allowed to travel into and out of Incomplete Creation and others like it in my old rules set). The Originals created a series or race of lesser beings to help them maintain and build upon Origin, called the "Secondaries" because they were second. Of course, the Secondaries rebelled for no explained reason, and destroyed Origin as well as most of the Originals; the Originals for their part annihilated all but one of the Secondaries (and that one escaped because it managed to hide somehow). The remaining 19 Originals repaired what little they could of the remaining portions of Origin, and this became the Voidsphere, the two Opposers, and the 19 multiverses, and they then created "Tertiary" beings (the Sidereals, in modern terms) who were later named Old Ones by the still lesser inhabitants of the reality-pockets they watched over. Eventually, the last Secondary showed itself, after turning a group of Tertiaries to its side, and started a new war which ended with its destruction (after being confined in the Positive Opposer, thus explaining why Positive energy is always proof against evil in any multiverse) and the destruction of most of its friends among the Tertiaries. Only 7 Originals were left after this, and they were tired of dealing with this existence after the war- so they left Incomplete Creation behind, "never" to return.
Reading the story today, along with the few rules I wrote to deal with the powers of the Originals, several things jump out at me. The most important of these is that I clearly didn't think much about what a being like an Original could actually
do with power able to create worlds larger than whole multiverses- my rules did say that Originals could simply ignore any attack sent against them by Power Points, or Life Points, but if that was the case, then how did any of the Secondaries or Tertiaries actually kill them? On a related topic, this is the first inkling in my old rules that these entities were so powerful that they could deal with true infinities- a concept that UK also adopted for his Eternals. The third thing to jump out at me is that the notion of that one Secondary working in secret to corrupt others away from the "goodness" of the Originals looks a lot like the Gnostic idea of the Demiurge trying to keep humans from achieving "gnosis" with true Eternity and the Aeons who dwell within it. The last thing to jump out at me is that, if these beings were immune to attacks, and didn't have any possible method of using their own special points to attack (truth: the rules state that the Originals can't use their version of Life Points for any sort of attack or combat), then what the Hells would one base a game featuring them on, exactly? It doesn't really make for exciting story possibilities.
The rules written down in that old notebook of mine don't state point-blank that Old Ones are made of quantum probability, but I know that I had the concept in mind even then- and the rules do say that there are "theories" regarding it and that it's "more fundamental." I'm pretty sure I wrote them that way because I intended that if I ever ran a game featuring Old Ones vs. PC Immortals, I wanted to keep the secret of the true nature of the Old Ones back for an exciting in-game reveal, but that's irrelevant now. What's relevant is that, when the notebook gets around to discussing the nature of the Originals, all it says is "Originals, in their elementary form, are thought to exist as pure intelligence with no housing whatsoever." And that's the best I ever came up with to describe what they really are.
Today, given the science-looking puzzle I've cobbled together explaining the nature and existence of the Sidereals so well, I still have no good answer to the question- but I have one possible avenue for explanation. Modern information theory, as formulated by Shannon in the 1940s IIRC, essentially states that information is the reverse of entropy. Now, some scientists today suggest that our own universe may in some manner be a construct of "pure information" at its most fundamental level; that is, beneath all the talk of particles and waves and quantum probability and strings, what's really going on is a process of bits and qubits (the quantum version of bits, used in quantum computing) interacting with each other and somehow producing everything we see and think and are. If this (admittedly vague and unsupported) idea has truth in it, then this substrate of pure information would be the "next step" of "fundamental-ness" beyond the quantum probability that I postulated Sidereals to be made of. In other words, Sidereals and everything they create or do are merely "programs" running on some underlying substrate that gives them an arena to live and work in, and everything builds on that base of information exchanges to produce the Reality that we see. Of course, if that substrate can produce intelligence at all (which it demonstrably can, since the Sidereals are clearly intelligent, as are the beings such as gods and mortals that they create to live within themselves), then it's not much of a leap to suggest that it might be intelligent itself. It might be conscious of everything taking place within its own "body" of information.
This notion, of each Eternal being literally a "body of information," also gels well with what I (through SEPHIROSOPHIA) told the PCs at the end of the campaign: that if they passed through the Final Gate, the "stories growing within them" would have a chance to "grow" and "Become." Stories are really just constructs of information, after all. If the true meaning of Eternal existence is a move to becoming pure information, and the idea is that the information of one's own mind acquires
life and
Reality in its own right, then surely this explains SEPH's comment: any stories growing within the minds of a being who (literally) writes its mark upon Eternity must become as real and alive as the being who is doing the writing. Simply by passing through such a portal, and becoming Eternal, a being would begin to spin stories and lives living within the information substrate that is its new "body." This, then, is the ultimate meaning of Transcendence. Doesn't sound so bad, eh?
Enough of esoteric speculations. Most of you probably didn't do more than skim all that anyway, did you?

You're wondering what rules I came up with for the Demiurge and greater Eternals. I adopted UK's "stages" of Demiurgedom for my Reality, and built on that to produce the Time Lords and higher ones. Here it is:
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Demiurge Stage I (120 DR, 26 KR, 1 TR): 40000 HD, 100,000,000,000,000,000,000 QP.
Demiurge Stage I (120 DR, 27 KR, 1 TR): 40000 HD, 200,000,000,000,000,000,000 QP.
Demiurge Stage I (120 DR, 28 KR, 1 TR): 40000 HD, 400,000,000,000,000,000,000 QP.
Demiurge Stage I (120 DR, 29 KR, 1 TR): 40000 HD, 600,000,000,000,000,000,000 QP.
Demiurge Stage I (120 DR, 30 KR, 1 TR): 40000 HD, 800,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 31 KR, 2 TR): 60000 HD, 1,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 32 KR, 2 TR): 60000 HD, 1,600,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 33 KR, 2 TR): 60000 HD, 2,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 34 KR, 2 TR): 60000 HD, 3,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 35 KR, 2 TR): 60000 HD, 4,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 36 KR, 2 TR): 60000 HD, 8,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 37 KR, 2 TR): 60000 HD, 6,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 38 KR, 2 TR): 60000 HD, 7,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 39 KR, 2 TR): 60000 HD, 8,000,000,000,000,000,000,000 QP.
Demiurge Stage II (120 DR, 40 KR, 2 TR): 60000 HD, 9,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 41 KR, 3 TR): 80000 HD, 10,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 42 KR, 3 TR): 80000 HD, 16,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 43 KR, 3 TR): 80000 HD, 20,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 44 KR, 3 TR): 80000 HD, 30,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 45 KR, 3 TR): 80000 HD, 40,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 46 KR, 3 TR): 80000 HD, 50,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 47 KR, 3 TR): 80000 HD, 60,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 48 KR, 3 TR): 80000 HD, 70,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 49 KR, 3 TR): 80000 HD, 80,000,000,000,000,000,000,000 QP.
Demiurge Stage III (120 DR, 50 KR, 3 TR): 80000 HD, 90,000,000,000,000,000,000,000 QP.
Time Lord/Aeon (120 DR, 50 KR, 4 TR): 100000 HD, 100,000,000,000,000,000,000,000 QP.
Time Lord/Aeon (120 DR, 50 KR, 5 TR): 100000 HD, 120,000,000,000,000,000,000,000 QP.
Time Lord/Aeon (120 DR, 50 KR, 6 TR): 100000 HD, 160,000,000,000,000,000,000,000 QP.
High Lord/Duad (120 DR, 50 KR, 7 TR): 200000 HD, 200,000,000,000,000,000,000,000 QP.
High Lord/Duad (120 DR, 50 KR, 8 TR): 200000 HD, 220,000,000,000,000,000,000,000 QP.
High Lord/Duad (120 DR, 50 KR, 9 TR): 200000 HD, 260,000,000,000,000,000,000,000 QP.
High Lord/Triad (120 DR, 50 KR, 10 TR): 300000 HD, 300,000,000,000,000,000,000,000 QP.
etc...
Yes, I end the real Table stored in the file on my PC with that "Etc." It's open-ended, just like the IH system itself. Honestly, not much need be said here, except that "TR" of course stands for "Transcendental Rank," and you'd essentially use the IH templates except for adjusting as usual for the much higher divine bonuses involved in my system. DR and KR were explained before, but TR is easy enough to extrapolate from them: each TR grants a +36 divine bonus to everything, +72 to all six ability scores, a Transcendental Ability (or 6 Cosmics, or 36 Divines, or 216 feats), and +180 Level Adjustment. I also decided to cap the number of KR at 50, since that's the point where a Demiurge reaches maximum growth before it can take the 4th TR and become a true Time Lord. I opted not to add DR or KR to any High Lord, because my concept of those beings is that when multiple Realities merge to produce one, only one consciousness is dominant- and that consciousness would remember its own history as a Demiurge above any other, so it would only have the DR and KR that it had during that growth. The TR, of course, are additive, and open-ended.
No being with TR was ever given full stats for my game, though I did put in skeleton-stats for the Demiurge (just in case) and for SEPHIROSOPHIA its creator. SEPHIROSOPHIA was postulated as having 150,000 hit dice, 150 sextillion QP, and therefore TR 5. I never actually decided what Transcendentals it had, precisely, figuring that the players would be scared off from fighting it by its 150,000 HD and clearly overwhelming power (and of course, I was correct).