Does anyone else remember the bit of information we got a while back about how the Abyss was formed when Tharzidun threw something terrible into the Elemental Chaos and it broke through the fabric of the plane? Well, think of it this way. The Abyss is like a hole in a piece of paper. On one side, the one we understand, is the Elemental Chaos and the realms of reality as we know them. On the other side is the Far Realm, a universe that does not play by our rules. If you think of the entirety of the planar cosmology as being contained within a finite (but so large as makes no difference) space, then the Far Realm is all that lies beyond it...or another sphere entirely seperate across the void...and the Abyss is the entryway or a wormhole, the place where the madness of that place has touched the elemental chaos. Just as when you stand in a doorway you are in neither room, so is being in the Abyss being caught between two alien universes.
The Far Realm is not a place of insanity, evil, destruction or tentacle monsters. That is just how our brains try to interpret the ab-light that ab-reflects off their ab-surfaces. Our brains simply were never rigged to perceive such things, so our minds go into overdrive, trying to conjure up something, anything, that makes more sense than what our senses are trying to tell us. Everything you experience in the Far Realms is a hysterical delusion crafted by your own mind in a vain effort to save you from true madness. Some people, especially the incredibly unintelligent and vapid, might even peer into the Far Realm and see nothing at all (Zaphod anyone?). Most people simply can't cope with the experience and lose touch with reality. If something so alien can exist, can be so traumatic to even attempt to perceive, truly it must be evil...or at least that is what we think. In fact, the Far Realm simply "is" in a way that nothing else in our universe "is" and may or may not care about us...we simply don't know, and we can't ask it/them.
Creatures such as Aboleths, Mind Flayers, Mooncalves and other creatures of the Far Realm are tainted by this universe. The powers which hold our universe together, decree that all that exists must conform to certain rules, rules of Magi-Physics and Alignment. Forced to conform, but railing at the very notion, they always result in hideous abominations, composite creatures out of nightmare that push the boundary of what is possible in our universe. Often, characters encounter such creatures before they visit the Far Realm, and thus, the guises of the Far Realm's lost children in our universe bias the thoughts of what the Far Realm will be like. Tentacles creatures become our frame of reference for the Far Realm, and so if we go there expecting them, then it is easy for our minds to dredge up similar images once it is faced with ab-reality.
You can also think of the Demons as being Chaos Cultists. They have looked into the Far Realm, and upon returning, they have gone mad in a more conventional sense. Unable to articulate the feelings of helplessness and terror, they act out violently against all around them. Their primitive minds simply cannot distinguish between the desire to fight or flee...and so they do both, attempting to move away from the Far Realm, deeper in our universe, and to take their misery out on us all.
It is not surprising then, that a few corrupted Primordials, the so-called Demon Lords would try and command the demons as an army, to give direction and purpose to their mindless violence by aiming it at the Gods and their creations. So fundamentally rooted in the nature of the world, and wise from their long existance and power, these Demon Lords dip into the Abyss while averting their eyes from the Far Realm. They lead by looking away from the gap, back toward our universe. It gives them enough focus and clear vision to keep on waging their war against creation. True, they seek to unmake all that has been made, but they do not seek to help the Far Realm's reality prevail. If they thought they had a chance, they might try to invade the Far Realm and extinguish it's maddening influence forever as well...perhaps they have tried and failed many times since the Abyss was born. Perhaps their impotence in being able to do so is what drives them to destroy this universe, a tangible, perceivable, comprehensible thing that they actually can destroy.
In any case, this is pretty much what the universe was like in my last couple of homebrews, and I will probably stick with something similar in 4e.
Robert "Thinks that you could easily put both The Demonweb Pits and Hell Into This Mess Too" Ranting
