"I dwell in your dreams; I savor your nightmares. Now you will serve me." ~Vaermina, Prince of Nightmares
"I am the princess of the night, thus it is my duty to come into your dreams." ~Luna, Princess of Equestria
Dreams are a powerful thing; there's a special sort of magic to be found in the realm of dreams, one that holds infinite potential. A beautiful dream emits a radiant light that comforts the one who conjures it.
A nightmare, on the other hand, holds dark magic that burdens the sleeper's mind, crushing them under its influence.
For a being who can feed on that magic, nightmares are a valuable source of sustenance. To a princess who watches over dreams, they can be a burden. When the one who feeds on dark thoughts turns its eyes toward Equestria, it falls to the guardian of the night to stop it.
After being freed from Order's curse, the Madgod Sheogorath is left without a home. He searches the many realms of existence for a creature whose Madness rivals his own. He finds Chaos instead.
After his victory over Chaos, The Madgod Sheogorath suffers the consequences of his time in Equestria.
When a dark cloud descends upon Equestria, its citizens fall into what seems like an eternal sleep, plagued with nightmares. It's up to Princess Luna to discover the cause and put a stop to it, before it's too late.