Monsterous Friends

Twilight walked though the field, her tail flowing though the wind. The purple alicorn was hosting the somewhat annual sleepover between her and her best friends and she has let the others know, except Rainbow Dash, whom she was heading to let her know.
Twilight stopped & looked up and saw Rainbow Dash napping on a cloud, she does that a lot.
"Rainbow Dash!" Twilight shouted out, hoping to wake the sleeping pegasus.
"Huzzzahwha?" Dash said as she sat up and looked around, a bit confused. She eventually spotted Twilight. Dash immediately spread her wings and flew to the ground. "Hey Twi, what do you want?" Dash asked as she landed.
"Just wanted to know if you were coming to the sleepover tonight?" Twilight said. "The other girls are coming. Also!" Twilight added. "There's gonna be a full moon tonight as well."
"Tonight?" Dash said as began to rub the back of her head. "I'm not sure."
"If you can't make it that's fine." Twilight said. "The others will understand."
Dash cupped her chin, as if she was pondering something. After a minute, Dash spoke up. "S-Sure, I can make. Infact, I got something to show you girls." Dash said, in a somewhat sad tone.
"Ok?" Twilight noticed Dash's tone, but as she went to say something, Dash had already flew away, leaving behind her iconic rainbow trail.

As Twilight began to walk home to the castle, she couldn't help but wonder about Dash's tone. It was sad, did Dash have something that would destroy their friendship? Was she futanari? Probably not. Was Dash involved with dark magic? No, Dash isn't a unicorn and Dash is too loyal to go to Dark magic. Come to think of it, all her other friends, even Pinkie, had a somewhat sad tone in their voice when they told her they would show up. Why? Where they scared of the full moon? No. Was Twilight just that boring? Twilight laughed at that thought. As Twilight walked into town, she decided to pick up extra stuff for tonight, just to help her friends.