(A/N: The song is called "Blue Lips" by Regina Spektor, hope you enjoy)

"We're heeere~!" Mabel sang, flying in a circle around Dipper who stared into it.
He could swear he saw a few orbs of flickering light within the dark abyss of the cave.
Mabel took off her sweater and placed it by the wall of the cave carelessly, letting her wings shake out and be free. She giggled as her wings fluttered.
Dipper took his contacts out, putting them back, glad he could be himself. His fangs grew again, his skin pale.
"Come on, before you become an inferno!" Mabel teased lightly, flying in, Dipper walking in after her.

The cave was very dark, Dipper's footsteps echoing through the huge walls of the cave.
Small gold orbs of light came into view as well as silver, pink, blue and purple lights, almost every kind of coloured light was drifting through the darkness, Mabel seemed to have a golden light emitting from her body. Dipper flinched a bit as to how bright it was, taking cover in the shadows.
He then heard some squeaking coming from above him.
Dipper looked up, wondering if he was hallucinating; above him were a group of bats hanging upside down from the cave ceiling who looked at him, chirping and squeaking in greeting, which made him feel a little calmer.
Mabel explored the cave, finding there was a small waterfall trickling into a rock pool in the middle of the cave. A few knotholes were in the walls where a couple of bats and other small elven and fae folk were nesting, and the cave on top was covered in grass, giving a beautiful view of the forest and lake below.
Dipper hung upside down on the cave's ceiling along with the other bats, turning into one himself with red eyes rather than the black or brown eyes the other bats had (the other bats seemed to look at him in interest), and looked at Mabel go into the pool before closing his eyes.

"WHAT DO YOU MEAN DIPPER AND MABEL ARE MISSING?!" Ford bellowed at Stan back at the Mystery Shack.
"I-I was doing the Mystery Tour and the next minute they were gone!" Stan explained.
"WHAT?!" Ford yelled, outraged at his twin.
"Well, sorry for doing my JOB!" Stan retorted with an icy glare, Ford mirroring Stan's angered facial expression.
"Well, come on! we need to find them before something happens!" Ford declared, running outside the shack. Stan groaned, putting on his gold knuckleduster and running after his brother.
"Mabel, would you knock it off?" Dipper's voice came from inside the cave, now in his 'human' form and on the ground.
"What? scared your bat wings will get wet?!" jeered Mabel, a little too loudly.
"No! I....uh.....it's none of your business!" Dipper blurted out, turning away. He didn't want to admit he had a problem with running water, especially with crossing it.
Sure, it was natural for vampires to have this fear, but he didn't want Mabel to know and make fun of him.
Mabel cupped some water in her hands and threw some at him, her twin speedily sidestepping the attack.
"Mabel! I told you to knock it off!" Dipper growled, turning around and facing her with glaring red eyes.
"Okay, okay, jeez!" Mabel sighed.
Ford looked up when he heard the voices. That must be where they're hiding! he thought.
"Ford, where are you going?" Stan groaned, his back clicking, before following Ford into the cave.
A few squeaks of nearby bats and the twin's whispering made Ford and Stan even more eager to see what was happening inside the dark cave.

Mabel hid in the rock pool, her body and wings beneath the water as the other fairies hiding in the little knotholes and dimming their lights so they didn't get seen, while Dipper turned into a bat and hid amongst the other bats, his own wings folded over his face.
Both their hearts beat faster as both Stan and Ford approached the area where they were hiding.