The shadow realm is clearly very different to any other realm or plane cus its not a physical place of its own but seems to be just another layer to other existing places. The fact that unlike all other planes/realms this realm is actively spreading from one place up does tell me it wasnt naturally there, so the question is what is making it and whats causing it to spread. Since they're making a point to say these giant shadow snakes are thriving in the deepest part of it (presumably where the origin of the shadow realm is) it does seem they very much they're connected to do it. Perhaps a queen/king leviathan or maybe it is something to do with xau tak or something?
I cant remember where i read about the dark beasts lore, been trying to look it up. Yes a "darker dimension" is rather vague but i remember reading it and thinking "this sounds like the shadow realm or something", need to find that book again. If zaros didnt use a leviathan to make his shadow stone but some weaker creature, it is possible he used 1001 dark beasts for it if they did come from there
As for iaia, you have to use some deductive reasoning to pin point it. Zaros first says iaia is in one of the lower planes, and from last year we know the lower planes are the old universes leftovers. We also know vampyrium, infernus and leng are other lower worlds and these are named as the blood, smoke and ice "runes", this leaves only shadow left (unless your counting wrath/miasmic which are now under question). Iaia has no visible stars cus last year we learnt the world has a VERY thick cloud cover, meaning the world is very dark with little sunlight, very fitting for a world of shadows. And finally the dragonkin seem to be related in some part to the ilujanka (i theorised a sister clan), so this again places iaia as one of the old universes worlds so would logically make it the shadow world most likely
10-Oct-2018 19:46:12