DISCLAIMER
LWD belongs to Canadian Television and Disney, and Supernatural belongs to the WB, which will soon be the CW. I got the German recited and the the Night Mare's form from a folklore and myth site, although I made up its other powers and any effects from the German incantation.
In her bed, Casey tried to steady her breathing. She had to pretend to be asleep, otherwise the Night Mare wouldn't show up. She wasn't worried about being affected again---Sam and Dean were in her closet. They'd never let anything happen to her. Plus, she had her own gun right beside her. In the closet, Sam tried to get comfortable, which wasn't very easy to do at his height.
"Dude, what are you doing? Trying to get ants outta your pants?" Dean asked, half amused, half annoyed.
"This closest isn't built for my height and my pistol is sticking in my back," Sam hissed.
"You got the safety on, right?" Dean checked.
"Dude, what am I? Three? Of course the safety's on," Sam responded.
"Good," Dean approved. The last thing they needed was his brother's gun going off and scaring everybody half to death, not to mention paralyzing the kid. Meanwhile, there was a soft whooshing and a whinny as something searched the house for a hole. It finally found one in the upstairs. The Night Mare gave a satisfied neigh as it zoomed through the hole. It silently trotted towards the room and entered through the small crack under the door. In the closet, Sam went rigid.
"Dean," he whispered.
"I heard it too," his brother confirmed. He slowly and cautiously pushed open the door, being sure not to make any noise. There was another neigh and the boys watched as a demon with a horse's head slid across the room.
"Bingo," Dean whispered. He and Sam removed their guns from the back of their jeans and waited until the Night Mare was on top of Casey.
"Freeze." Hearing the simultaneous click of the safety of two guns being released, the creature turned around. It began to flee.
"Hier leg'ich mich schlafen, Kein Nachtmahr soll mich plagen," Sam recited. The Night Mare hissed and turned in another direction.
"Bis sie schwemmen alle Wasser, Die auf Erden flieBen," Dean added. The boys watched as various objects in Casey's room began to shake as the creature's eyes began shine a bright silver. Then, they squinted from the brightness. They went to recite the rest of the incantation, but no sound came out. No! Casey! Dean's mind shrieked. No. Can't---can't let it get her, Sam thought. With a hiss, the NightMare placed itself on Casey's chest. To its surprise, her eyes flew open.
"Und tellet alle Sterne, Die am Firmament erscheinen! Dazu helfe mir Gott Vater, Sohn und heiliger Geist. Amen!" she chanted quickly. The Night Mare shrieked as everything became still and the shine in its eyes faded. It struggled, but found itself immobile.
"Gotcha, punk," Dean said. With that, he and Sam cocked their weapons as Casey brought out her gun. Then together, they all fired silenced shots. With one last shriek, the Night Mare disappeared in a cloud of black and red smoke.
"Well, thank goodness that's over with," Casey sighed.
"Yeah," Dean agreed. "You all right?" he checked.
"I'm fine. You guys?" Casey responded.
"We're good," Sam assured. She sighed in relief and Dean drew Casey into a hug and kissed the top of her head, thanking whoever was listening that everything had ended so well.
AUTHOR'S NOTE
Translated, the German incantation is as follows:
I lay me here to sleep;
No night-mare shall plague me,
Until they swim all the waters
That flow upon the earth,
And count all the stars
That appear in the firmament!
Thus help me God Father, Son, and Holy Ghost. Amen!
Yes, I realize it makes no sense, but I was using it as an incantation that would make the Night Mare powerless.