I'm interested... I've got the next 3ish levels roughly mapped out for what I think the party will do (I've built in hooks, and they've been good sports about biting so far), and I'm working in some Far Realms stuff. Would be cool for ideas that I can hint at now and use later.
Alright, here's some ideas. Usually the Far Realms is used as "It's dangerous because it just is, interacting with it is bad like merely being close to radiation is bad" or occasionally "It wants to because it can/likes to", which is similar to Demons and such. Instead, I propose that the
entire plane of existence needs to destroy Reality.
Imagine the Far Realms as a sea of raw chaos, with entities who exert control over that chaos. Let's say one of those entities just went to sleep, or went out of commission. What occurs is that in its slumber, amid all this chaos, a bubble of Order managed to create itself. That bubble of order? The world (and its planes). Reality is an island of law in a universe of insanity.
From the Far Realms' perspective, this island is a malignant tumor of pure
Wrongness that has to be stopped. It must awaken Reality's sleeping overlord. To do this it must exert influence. To exert influence, it needs to create enough chaos within our reality to be able to exist here. Each aberration in Reality, every crazy cultist ritual is increasing the chaotic atmosphere just a little bit more. Once it reaches that acceptable ratio of insanity, then the more powerful forces can enter, and all hell is going to break loose.
Psionics could play a role in this. Psionics could be either another branch of this turbulence - adding to the tole. It could be a defensive mechanism of Reality itself - psionics is a force to combat the Far Realms. Or it could be a bi-product.
[sblock=The following could work ON TOP of that]First, imagine that the Far Realms as a plane is
one immense being. The entire plane is alive, but it can't influence what's in its body anymore than we can control our core temperature or are aware of our individual nerves. All entities within the plane are some sort of organism with a role in this planar body, sort of like white blood cells, red blood cells, gut bacteria, etc. Reality is the equivalent of an organ that's no longer working, and the various antibodies of the Far Realm are trying to heal it (by fighting the cancer that is Order). Now, the final campaign goal, at level 30: go into the plane, find its source, and kill it. That is an epic level challenge.[/sblock]
Now this is a very, very Big Picture idea. I imagine that no single aberration has a good grasp of this. Even something moderately powerful that flops into our reality from the FR doesn't have the big picture. They all have their small part, but there likely exists an instinctive drive to squash Reality in every aberration. Probably this manifests as 'get more of us here' or 'defend other aberrations' or even 'corrupt native entities so they can help us'.
Also bare in mind that the Material plane likely won't be the only target of the Far Realms. The other planes would be just as susceptible (and, even if the Pcs are defending the Material, those other planes might start to fall, upping the tension). This might also give reason to go plane hopping - go, fight the corruptive spread of the FR in the Shadowfell and the Elemental Chaos. The Feywild would probably be the first and hardest hit - the Fey's magic likely has little influence on entities with alien minds not susceptible to tricks or emotion. So not only would the Feywild get corrupted, but the various fey would likely start flooding the Material in seek of safe haven.
