I'm not thinking about the tentacled appearence and Lovecraftian background, but rather its motivations. Usually, these are described as being unfathomable.
I hear 'unfathomable" or "so intelligent mortal minds can't conceptualize it" tossed around in fluff text for everything from Gods to Demons. And usually their plots are pretty easy to Fathom.
An alternative would be that the Far Realm seeks to absorb Creation, and "devour" it, turning it into an extension of the Far Realm.
Well yes. I think that's the most common usage, rather than "DOOM". The Far Realms is like the Borg, but instead of just people, it's EVERYTHING. It could be that the Far Realms is to Unnatural what the Abyss is to Evil. Demons are basically just the Elements corrupted by pure evil and chaos. Well, the Far Realms could be the same thing, except that it's just Madness and Chaos. Physics on LSD.
Any other suggestions as to what the Far Realm's motivations are?
I've seen a lot of cool ideas on ENworld over the years, lemme sum up. Problem is, if you adopt one, it's a rather world-defining one.
1) As the above, as far as "assimilation", but it's a lot more intentional and insidious. The above makes it seem like the Far Realms is just Insanity Radiation that effects everything. But instead, think of the Far Realms as intelligent and deliberate. The Far Realms can't "breathe our atmosphere", in terms of reality, so it needs enough psychic pollution or enough unreal reality in order to be able to step into the Real World.
This is what aberrations are doing. Perhaps not even consciously aware of it, but an Aberration just doing its thing (and hell, possibly MERELY EXISTING here) is paving the way. If left to their devices, the Far Realms will soon be able to survive/enter and assimilate.
This would then relate to psionics. Because Psionics could either be "pushing back" the psychic entropy, or psionics could unwittingly be doing the same thing! So a situation where all Psionics could be reality Defilers, or they could be the Purifiers, to put it in Dark Sun terminology.
2) The Far Realms itself is a plane-sized organism. Its body is too big to comprehend. But it is in fact one entity. [i}Everything[/i] that lives in the Far Realms, therefore, is an organism of that immense body. They are the cells, the antibodies, the digestive bacteria, the enzymes, stomach acids, and parasites. They all have an instinctive role.
So the activity of the Far Realms and Aberrations isn't that there's an over-arching motivation, but it's biological. To the Far Realms, "Order" and the natural (as far as we're concerned) is a cancer.
We are the cancer. And where the Far Rralms bleeds over into us, that's actually where It has a tiny wound (so to speak), and our disease is getting into it. Therefore, the influence of the Far Realms isn't offensive, but defensive; its body responds by trying to stop the cancer (or turn it into itself, to neutralize the cancer).
This immense body is, for all intents and purposes, "asleep". It's not conscious because it's not awake. If it were woke up... This also opens the door for the Campaign's epic ending being about slaying the Far Realms. Because such a task would require 30th level PCs.
3) Using the above example of reality as cancer, but let's change the analogy. Imagine the Far Realms as a continent with lots of little countries. Now, imagine that in one country, the ruling authoirty went away. No one replaced him, and the country broke down. No authority, no one in charge, it's just unchecked.
Now, imagine that anarchy is Order. Logic. Physics. Our world, basically is a pocket of Law within a vast sea of Chaos.
Finally, imagine two things. 1) The Authority (the one that left) is asleep. What happens if it starts to wake up? 2) What if the Far Realms (or other Authorities) become aware of this, and want to ride in and take over? Or even that the original Authority never left, it merely changed its dominion
into the world. What if someone wanted to change the Authority's mind?
4) This fits in with #1, but works fine on its own. The Far Realms could see the Real World as an untapped, natural resource. Of course, the resources they are looking for are dreams, thoughts, emotions.