Mustrum_Ridcully
Legend
I can't give you an unfathomable motivation.I'm not thinking about the tentacled appearence and Lovecraftian background, but rather its motivations. Usually, these are described as being unfathomable. However, very often it just boils down to "destroy the universe". This is very boring, IMHO, and it makes the star-creatures a bit too similar to demons (who are the ultimate "destroy Creation" type of entities in D&D, whereas devils seek to enslave Creation). An alternative would be that the Far Realm seeks to absorb Creation, and "devour" it, turning it into an extension of the Far Realm. (This reminds me of the Tyranids from Warhammer 40K.) BTW, I really like the idea that the stars in the default D&D world are actually malevolent, sentient entities.
Any other suggestions as to what the Far Realm's motivations are?
Well, I could. Illithids want to kelvire the tridoxkuf and enjoy belsom kiffani turkas. Unfortunately, it's even unfathomable to me what this is. I just know it requires them to eat brains and conquer the world.
A "unifying" theme of the Far Realms might be that there is no unified goal. The different aberrant creatures all act differently. We just "know" that they don't come from here, and that the laws of physics (including magic) don't work like ours. How they can even exist here? No real clue. It seems as if they are capable of adapting to our laws - but some are also capable of adapting our world to their laws.
Some seem to have the goal of getting more inside our world. Some seem to have the goal to get out. Some seem to desire conquest. Some seem to desire destruction.
Maybe they all actually follow the same goals (but why do they fight each other occassionally?). Maybe they all have different goals. Maybe even those that seem to cooperate? Who knows? Pi is probably 3i in their world, at least on sundays if they fall on a wednesday after yotz.