The Bloodlands are a naturally occuring biome, like a desert or a forest. They are believed to be magical in origin because of their unique and horrible traits.
Bloodlands are areas where necromatic energies swirl. The sky often rains blood, bile, and other bodily fluids. When storms are particularly strong, chunks of rotting meat and bone fall like hail. These weather events are quite common, and don’t seem to follow normal weather patterns. Aside from the horror of the sight, many predators are drawn out by these storms and feed upon the body parts that fall from the sky.
The most dangerous trait is the frequency of necro-storms. These events are usually preceded by a thunderous sound like the beating of a giant’s heart. Then the clouds form a cross between a tornado and a tentacle; a tunnel of wind, blood, disease, and dead bodies that snakes across the landscape. The carcases that fall from these malevelent vortexes are very much dead, but very much alive. Zombies, skeletons, and other types of undead pour down from the sky to stalk the countryside.
Though the rains and storms themselves seem to be limited to certain geographies, the creatures that fall during necro-storms are not. Villages that live near these lands often mobilize their militias to address the threat of wandering undead.