Eventually, the undead conquer the entire world, and finish off all the living creatures. Inevitably, that means blotting out the sun, whether via a permanent eclipse, never-ending cloud cover, or other means. Who favor the night, and wield powerful magics to turn the world into something more to their liking.

But over time, the fast-replicating first wave is replaced by an empire, dominated by intelligent undead. Which always starts with a contagion, a breed of undead that multiply quickly enough to overwhelm demihuman and humanoid civilizations. And what causes worlds to die, in such great numbers that the mu are needed? The plague known as undeath. They're the ultimate tools of the gods of the earth and growing things, sent in to restore life, when a world dies. Help it decompose, and become fertile again. Who start as spores, but that's not the proper term for their epic fruiting body. But the mu are fungi, so they lack photosynthesis, the basis of all life under the sun. Click to expand.Terran is earth, which in mythology is almost universally associated with fertility.