Unlike all other realms Blight City is not a true realm, it is an aberration in the skin of reality the Skaven have burrowed into like so much rock and dirt before it. Constantly attempting to cave itself in or topple the city entire, teams of Skaven work day and night to not only maintain but expand their sprawling warrens and great burrows. Filled with ramshackle buildings, rotting scaffolding and pollution belching factories, laboratories and refineries Blight City is a monument to Skaven ingenuity and cruelty. Life is cheap in Blight City and nothing delights the Great Horned Rat more than that.
What do you get when a species of the most devious, selfish and deluded man-sized rats of all time imagine a god for themselves? You get an even bigger, more devious, selfish and pure evil god sized rat. The Great horned Rat is the incarnation of ruin and destruction caring only to gnaw at the roots and cloth of reality to turn it to not but trash and ash for their burrows.
The lore of Ruin is not a result of magic diverging It is a result of the Skavens meddling and their worship of The Great Horned Rat. Ruin is simply magic designed to despoil, pollute, corrupt and destroy. It has no other purpose, no true nuance, just a mindless desire for utter ruination. As Ruin is more a faith-based magic it has no realmstone instead Skaven Harvest a substance called Warpstone, which is the pure solid stuff of true chaos, mutation and transformation aplenty sprout from this subatnce. Skaven uses it as fuel for machines, deadly ammunition, forge it into weapons and even consumes the stuff recreationally for its mind altering and mutagenic properties
Its a rat eat rat world, skaven are born in the dozens and many consume their siblings as they feel the gnawing eternal hunger all skaven feel. from there they rush to prove themselves worthy of ascending from common cattle slavehood into a clan member of one of the hundreds of great clans of skavendom. those born of black fur are trained as storm vermin while those of grey fur are trained as wizards by the grey seers. skaven society is ruled by a council of 13 with two seats for the grey seers and one open seat for the great horned rat
Skaven-Fiendish rat men, cowardly and savage they swarm in large numbers and steal technology they turn against their foes