Dipper marked Cassie on their second year of knowing each other or so bc he's an overprotective nerd and she fucking summons demons to help with homework. No demon would dare mess with her bc hELLO THERE ALCOR'S PROPERTY BITCH, and Cassie wouldn't even realize it until that time a shitty ex tries to sick a demon on her and the demon literally sees her and goes 'nOPE THE DEAL IS OFF FORGET IT I'M OUTTIE'. He then tells Cassie who summoned him (to save his own ass of course) and rUNS.

post/107186382048/i-headcanon-dipper-marked-cassie-on-their-second

Cassie had been summoning Alcor the Dreambender for help with schoolwork for a year, before expanding her summonses to include both schoolwork and just to hang out for a second year. Sometime during the third year, she was granted his proper name, alongside the end of the lectures on summoning demons and a good measure of trust going both ways.

A few summonses after that, Dipper paused in the middle of a giggle fest to look at Cassie strangely.

Leaning forward, he brushed a kiss across her forehead. Her hand flew up to cover the spot, which had tingled for a second, and she gave him a look, taken off guard by the surprise affection.

"What was that for?" she demanded. He shrugged, tossing some popcorn at her.

"No reason," he said airily. "Just...because I could. And because I care."

Cassie blew a raspberry, throwing popcorn back at Dipper. It started an all out popcorn fight, and the random kiss was forgotten.

Being best friends with a demon made dating...interesting. Most of them Cassie had one or two light dates with, never anything serious, just testing the waters. Dipper may have been in a class of his own, but he was still a demon, and Cassie wasn't willing t risk either her or his safety. She'd rather keep her best friend, demon or not, than any of the people she'd gone on a date with.

Then she tried dating Scott, and, well...he decided things were far, far more serious than they were, far faster than Cassie was comfortable with.

The break up wasn't pretty. Cassie hadn't thought they'd gone out enough to even warrant a break up, since two dates did not engaged make, but apparently Scott had other ideas.

It had been two months since Cassie had broken up with Scott, and to be blunt, she had mostly forgotten all about it.

Until, in the middle of the night, when she was alone in the house, she was woken by smoke and flames and glowing lights in her bedroom.

She'd thought she was used to demons manifesting in her room.

She was wrong.

The demon in the center of the smoldering circle scorched into Cassie's carpet didn't even remotely resemble a human. Too many arms, too many eyes, some sort of abomination created of nightmares crouched, still smoking, too close to her bed.

It grinned at her sadistically, running a too long tongue over too long teeth, eying her hungrily.

Cassie pressed herself against the wall, groping for the circle on her nightstand, voice frozen and heart pounding so hard it felt it would force its way out of her chest, silently screaming for Dipper to come help her.

The demon in the circle took a step closer, then its eyes darted up to her forehead and it froze. Its mouth formed silent words before it skittered back, like a small frightened animal, away from the stunned Cassie.

"Oh ́n̡o. N̨o. ͟N̸O͝PĘ. NOPE̷ TH̛IS̵ ͘AIN'͝T W̕ORTH͠ ͠I̡T I ͢A̷M OUT͡.̷" they gurgled, still skittering away. "So͜rr͝y s͟orr͝y ͏j͟u̕s̨t g͟onna̡ ̸l͘eav͠e d͟o̴n̛'҉t̵ téll Al̴cor DO͞N̸'T TELL ͘A͟L͞CƠR͝ P̵L̸E͞A͠SE͢"

"I won't tell him it was you if you tell me who summoned you and why," Cassie said quickly, before the demon could disappear. She'd demand Dipper tell her how they knew about him later.

They nodded their head quickly, like a marionette. "O҉k̀ày okay̸ f̛ai̸ŕ d̢e͘al̛ fąi͏r e͟n͢o̡ugh ̛- ̴me͘a͟tb͜a҉g̛'̀s ́na͟m͘e̷ ͟w͢a̵s ҉S͡çott̵ ̕B̡e҉a͟uch͞a͟mṕ, ̴w̨a̷nt́ed̶ ͘t͟o 't̷eac͡h yo͏u̴ ͢a le͘ss̛on'͏ and h̛a̛v̶e a̛ sc̡a̴r͡e ͏an͘d҉ ҉p͜ret̀end̶ ̕t́o̧ re͜s͝c̸ue ͡y͝ou̸.̷ Sho̢uld be͠ co̕mi̡ng b͞ỳ so̷on." It paused, adding almost pathetically, "Can I͘ ͞go̵ ͢n̵ow҉?"

Cassie was not one prone to fear or to anger. In fact, it was hard to get her angry sometimes, and as for fear, well, she'd summoned a demon for math help. So when she saw red now, still shaking with adrenalin and fear of the demon in her room, it was enough to finally bring Alcor roaring into existence, already covered in void black and with fire spilling from eye and claw.

He saw the demon cowering on Cassie's rug and lunged, his roar of rage cut short by Cassie's cry of "No, don't!"

Dipper pulled up short, claws barely an inch from the other demon, who disappeared the instant he paused, leaving faint claw and scorch marks behind.

"Cassie? Why did...it got away!" Dipper said, glaring briefly at the spot where the other demon had stood before starting to fuss over Cassie. "What's going on? Are you okay? Shit, I was too slow, I'm sorry, but why..."

"Scott," Cassie growled, and Dipper paused.

"...isn't he that guy you had like two dates with a couple months ago? The one who thought he could tell you what to do?"

"Yes," she said, blankets bunching under her hands. "He sent that demon, to 'teach me a lesson' and let him pretend to be a hero. Then it just stopped when it saw me and said the deal wasn't worth it and started begging me not to tell you." She gave Dipper a glare, though her heart wasn't in it, most of her anger still directed at her ex, fear cooling now that Dipper was here. "How'd it even know about you?"

Dipper scratched at the back of his head like the goober he was, shifting uneasily. "Um...I might have...marked you? When I kissed you? So other demons and stuff would know you were under my protection?"

Cassie's mouth opened and closed a few times before sounds from downstairs cut her off. Dipper's ears twitched, and he said, "It's Scott, ready to come play hero and wondering why it's so quiet." He raised a claw covered hand and grinned, mischief sparking in his eyes, meeting Cassie's raised eyebrow with a grin. "Want to give him a scare and a lesson instead?"

The slowly growing grin on Cassie's face was almost as evil as Dipper's, and for a brief second he wished she could have met Mabel – they would have been a force to be reckoned with. "I knew there was a reason we're friends," she said. "Now cover your ears, I scream loud."