Surrounded by turnips.
Under the newly recovered green forests of Ghyran, the Flesh Eaters have retreated and live in tunnels and caves. Far from the underground empire they once were, the net of tunnels is now almost empty, losing part of their control to other subterranean races like Skaven and Night Goblins.
They are besieged from all sides: Above the ground, old human kingdoms have recovered their former strength, thriving on the abundant crops brought by Allariele's magic. From below, Skaven and Goblins try to push them out of the tunnels.
But that wild growth had worse effects on the Flesh Eaters: Food sources like graveyards, burial sites or mass graves are now invaded by giant trees, whose roots have made the corpses unreachable from below, cutting the meat supply for the underground dwellers. But the unstoppable wild growth keeps expanding downwards: Huge roots block or collapse the tunnels, while thousands of edible tubers grow deep in the earth, decorating the Under Empire walls like constellations, as a mockery of the Dwarf Holds of old, where gems and crystals were used on the stone to mimic the night sky over the builder's heads.
With a disgusted face, the captain of the guard smashed the Nightstone with his sword's pommel. "Bring more volunteers, Teebald. Almost the entire north wall is covered in this filth. We need to get rid of those stones before the whole wall crumbles.
As the above realms heal their wounds caused by the War against Chaos and recover from the famine that came later, almost all the megafauna has disappeared, giving ground to giant insects (specially Coleoptera like the infamous Wardroth Beetle). Without their usual food source, creatures like Nightshriekers got smaller and more feeble, making them unfit to be ride into battle by Flesh Eater Knightly Orders like the Morbheg Knights. Luckily for the cannibal hordes, an unexpected pack of allies has shown up at this dire moment.
The knights arrived when the sun was higher. The Captain almost drop the water pot when he saw them. Their gleaming armor and the double handed swords they brandished were the envy of the army, but what captivated all the settlements' attention were the lions. They were huge as they were regal, with long manes decorated with crystal beads. They said the lions were magical creatures, but the Captain knew they were more than that. He had listened to stories about their resistance to spells, some even said they could reflect dark magic against the caster. But their most important ability was to purify and cleanse the land. When they were close, the Nightstone outcrops withered and crumbled to disappear in minutes, just like light defeats darkness with its only presence. The three lions growled as the dark rock started to disappear, then roared like thunder as the Nightstone was no more. Everyone cheered and saluted to the knights as they turned and walked south on their fierce mounts, but the Captain knew they would be needed again sooner than later.
But the Nightstone is nothing more than an illusion. There are no magical black rocks tainting the land. Just earth and plants.
Vegetation grows rampant above and under the earth, so enormous turnips, potatos and other root vegetables are found anywhere. As the Flesh Eaters burrow the earth and build new tunnels they find those tubers and are sickened by their size and smell. But those same tubers attract other beasts who compulsively feed on them, like the wild boars of Ghyran. The tusked beasts grow bigger and more dangerous as the raw green (and addicting) magic in the roots empowers them. That symbiotic relation between the wild boars and the Flesh Eater's tunnel's turnips has been capitalized by the knightly order of Morbheg, whose members see the fanged furry monsters as benevolent regal lions who let the knights ride them to battle.
In the same way, the Flesh Eater repulse against every food that's not raw meat coalesces in their collective deranged mind as the feared Nightstone of legend, a stone that magically disappears in the presence of the lions.