Why Shadows don't end the world

10.2.4 Pools of Deep Shadow
Veteran players of Dungeons and Dragons often ask “Why don’t Shadows just take over the whole world?”
Certainly, there are very few residents of the worlds of D&D that can fight against a Shadow at all, and their
victims rise from the dead as Shadow Spawn, so it doesn’t take a lot of imagination to see where this is going.
However, there are a few things limiting the growth of Shadow armies that are not mentioned in the core
books at all.
The first is that only intelligent creatures slain by Shadows turn into spawn. That’s important, as it means
that Shadows cannot simply hunt frogs in the swamp until they number in the tens of thousands before they
roll over cities and dragon caves like a fog of Death Incarnate.
But perhaps even more importantly is that almost any time you see a Shadow, or for that matter any
incorporeal undead creature, you are looking at a summoned creature. When the Shadow’s summoning ends,
all of its spawn vanish. Most of the time, an incorporeal undead is summoned forth from the Negative Energy
Plane by an object that looks much like a puddle of very oily water, called a Pool of Deep Shadow. Whenever
light falls directly upon the pool, or the sun rises high enough in the sky that there are no shadows (about half
an hour before and after noon), the summoning effect ends and the Shadow vanishes. When the shadows grow
long and darkness has fallen upon the pool, a Shadow is again summoned.
This means that an individual Shadow or Wraith has a very difficult time destroying the whole world, as
there is no particular way for them to get more than a day’s float from their pool. It also means, however, that
areas inhabited by Shadows are extremely dangerous – for even if such a creature is destroyed it will return
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again the following day. And on every day it will return until those charged with exterminating it are caught
unlucky or unaware. In order to permanently destroy such a pool, a flask of Holy Water (or Unholy Water) need
simply be poured into it, causing the blackness to depart and the water to become quite clear and drinkable.

Why Shadows don't end the world

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