This just came to me and since there is barely any of this crossover so why not?

I will be updating some of my other stories too.

Mostt of the undertake characters look like the ones from Quantumtale and some are from the au

The shippings in this story are of my own choice if you don't like the shippings I pick, then you don't have to read it

I don't own Undertale or Star vs the Forces of Evil

"So how did you guys' date go?" Asked a boy in a hoodie. He seemed to be 15 years of age and 5'9". He had messy and spiky silver hair that reached half way down his neck and the bangs (that also looked spiky like an male ((or female, not judging)) anime protagonist) reached his eyebrows. He had white irises with black scleras and pale almost white as snow 'skin'. His attire consisted of said hoodie that is black with plum blue lines running along it vertically (which is currently unzipped) that had white fur around the hood of it (he has it down), a dark blue T-shirt underneath, black and plum blue cargo shorts that reached past his knees, black circular goggles on his forehead, normal fingerless black gloves, an aqua blue bandana tied around his neck with strange symbols on it, a black backpack, and black and dark blue shoes (the outfit for the oldest version of TK Sans except the goggles aren't cracked. He will also change clothes sometimes). One would find his attire normal or average, that would be the case...

If he wasn't standing in the snow while it is still snowing! However he seemed unfazed by the cold weather while he looked upon two of his friends.

One was a boy who is 14 coming on 15 with tanned skin and blue irises and normal white scleras. He was 5'8" He had dark brown hair with a hair style similar that of his friend's. His attire was a long-sleeved baggy shirt that was blue with horizontal purple stripes on the chest, dark blue pants, dark blue shoes, and due to the weather he also had on a purple beanie, a purple thick jacket, and dark blue mittens.

The other was a girl same age as the boy with slightly pale skin with dark brown eyes and one large slightly pink dot on each cheek. She had light brown hair that reached to just below her shoulders while the bangs an inch above her eyebrows. She was 5'8" to. Her choice of clothes was a long sleeved green shirt with horizontal dark yellow stripes, a brown skirt that reached to her knees with black leggings underneath, short brown boots, a green double laired jacket, a green beanie (she likes green), and very light yellow mittens.

These two were Frisk and Chara Dreemur. Ambassadors to the monster race, adopted children by King and Queen, Dreemur the only existing humans with a Determination SOUL, and saviors to monster kind. The white haired teen is Sans the Skeleton. Yup you heard right, Skeleton. Some monsters actually look somewhat humanoid and skeletons are one of these monsters. They look like they have skin but that is actually bone just thicker and differently shaped than a humans. This also explains a few different physical features of his. He is incredibly intelligent for his age, likes to sleep, is unusually lazy, easy going, a punmaster as he calls it, helpful when his friends need it.

Frisk and Chara blushed while they still held each others hand looking away slightly muttering "good". Sans chuckled. They started dating recently (no they are not siblings nor were they raised around each other) and they are still nervous or embarrassed on the subject.

" Well anyway you know when the others will be here?" Sans asked and right on que the rest of his friends came running up to them apologizing for being late.

Alphys she is shy, likes anime, watching Undyne fight and talking to her, hanging out with her friends, and working in the labrotory her and Sans work with Dr. Gaster (Sans' dad). She is currently 14 years of age. She is 5'5". She looks a little more monster than the rest except Undyne with yellow skin green eyes with glasses. She looked slightly like a dinosaur or lizard with her yellow hair the way it is. Her clothes are a thick wool long sleeved grey shirt over a red T-shirt, a lab coat over her shirts, had a white toboggan on her head, light blue thick pants, and black shoes.

Undyne likes to fight, train, watch anime, hang with Alphys, and challenge Prince Asgore Dreemur because he is the strongest of their generation physically and magically. She has just turned 15. She has persian blue skin, gills, and slitted yellow eyes. She is 5'9". The clothes she is wearing is a sea green sleeveless corset (made of thick leather to be used as full training armor), a black long sleeved shirt (after much convincing), black cargo pants with neon green stripes diagonally going inwards over the cargo pockets, an eyepatch over her left eye (to look cooler), and black and red cargo boots.

(Prince) Asgore Dreemur has blonde (golden colored) hair and brownish eyes and is 15 and a half. He is 5'11". He likes tea, helping people and monsters, and practicing being king and his skills. His clothing consists of a black shirt with purple sleeves, his crown, a black cloak with iron shoulder plates and the family symbol on the back, black pants, and black steeltoe boots.

Toriel has white hair and red(using magic)/pink eyes(normal) and she is the same age as Sans. She is 5'9" and a half. She focuses on fire and healing magic, hanging out with her friends, likes working with medics and helping others, and tagging along on some of Sans' missions for Dr. Gaster when he let's her. She is dressed in a violet (on the sides) and light purple (front and back) dress that reaches to her knees and has sleeves, dark violet sandals/boots, a pink light scarf, and a pink thick jacket with white leggings. She has a crush on Asgore (much to the dismay of some certain people).

Papyrus the Skeleton is Sans' younger brother with the same white hair and the same eyes. He is 6 years old. He is 3'7". He likes to practice summoning bones attacks, making puzzles, playing with the others, and making new friends. He wears grey skiing goggles with orange lens, an orange long sleeved shirt, a red jacket with a orange skull on the chest, baggy brown pants, red winter boots, a red and yellow backpack, and a red scarf on his neck.

Gorgette is a month younger than Toriel, has a huge crush on Asgore, calls Sans a windbag, is rivals with Toriel, (has got into countless verble and physical fights with her). She has green skin and green hair on the front of her head but snakes at the back of her head that normally stand up and is noticeable that also react to her powers and emotions (since they do what she says she has never once had a bad hair day), she also has light golden yellow eyes (which the left one is covered up by the normal green hair), and slightly longer canines almost fang like. She wears single strap violet dress that stops at her mid thighs, she has a gold headband, sideways 'S' marks on her cheeks, violet sandals, a purple toboggen over her snakes and hair, holds a small purple purse, and a light purple jacket. She is 5'7".

Grillby is a monster made of actual fire (but is somehow able to touch most objects with no fire damage) and is 15 and 1/4. He is Sans' oldest friend, works in his family restaurant/bar, is one of the more serious of the group, but likes games. He wears orange goggles that look like sunglasses just thicker on the handles and go all the way around, a black vest with a long sleeved white dress shirt underneath, black dress pants, and black dress shoes. He is 5'10".

Mettaton is a pink female ghost/monster that's the same age as Papyrus... That's pretty much it she doesn't wear anything (look it up Quantumtale Mettaton). (Not counting levitation) she is 3'6".

(A/N most of them look like the ones from Quantumtale with some of their outfits crossed over)

"Hey Sans." Said Toriel waving to her best friend/pun buddy. Sans' smile widened "Sup Tori? What took you all so long? I thought you guys were excited to come with me." Undyne answered "Oh well since we are heading into the unknown I packed some extra stuff. Annnnd Gorgette took forever to put on something and 'make-up'" she said with annoyance at the last word.

Undyne never liked putting on make-up. Even when she was still using to pretend to be 'prim and proper' around her dad who believed her to be his 'little princess'.

"Hey! Beauty like this doesn't happen on its own! Right Asgore~?" She said in a flirty tone at said prince who chuckled nervously while Toriel glared slightly at her. Sans decided to save his friend by changing the subject "Um guys? We are on a time limit here." He said pointing to a nonexistent watch on his hand.

"Oh right! Come on nerds we gotta hurry!" Undyne shouted picking up Alphys and Papyrus then placing them on her shoulders. "Eek!" Alphys squeaked blushing. "Wowie! To the lab!" Shouted Papyrus while pointing ahead.

With a war cry, Undyne charged toward the lab with a cheering Papyrus and a blushing Alphys on her back leaving the others in her dust-er snow. "Hey guys wait up!" Shouted Asgore who started after them with everyone else behind him except Sans and Toriel. He looked at her.

"Wanna take a shortcut with this bonehead m'lady?" He asked bowing slightly and extending his hand to her in a mock fashion putting emphasis on the pun. She giggled "Why yes sir Sans I would be delighted." She said taking his hand as they walked in the opposite direction the others went.

Then they vanished with the falling snow blocking the vision of any onlookers.

In another galaxy inside Butterfly Castle

Marco Diaz , this afternoon, currently attending his duty as Star's squire sitting in his room at his desk organizing a schedule for her princess duties, doing paper work on basic needs for the Mewmans, helping writing laws on Monster rights, etc. She was out on a date with Tom.

Just thinking about it filled Marco with anger, sadness, and depression. But he shook his head and tried to focus on the task at hand. Tom and Star are his friends. He doesn't want to ruin things between them by confessing his feelings. Besides he had his chance but he was to stupid to realize the truth, to little to late. Their was also the case of how he couldn't help Tom and Star fight Mina at the Monster Bash, they found out about Meteora Eclipsa's daughter, and the monsters got the short end of the stick in the end of it all.

He stopped writing and decided he needed to get some air to clear his thoughts.

He soon found himself in the rose garden of Butterfly Castle sitting on the bench just looking at the sky thinking about how difficult things have become recently and how much pressure Star must be feeling. He heard something to his right and turned then seen Eclipsa with a much smaller chain on her leg since the trial, she also had tear marks on her cheeks running over her spade marks. "She must have been crying. She must have learned about Meteora." Marco thought feeling a little bad for the 'Queen of Darkness'. He can't blame her, her daughter is alive but is missing and reports of her rampaging around all of Mewni.

"Is this seat taken?" Eclipsa asked barely above a whisper. Marco scooted slightly and patted the seat next to him, he was weary of her but he wasn't heartless. She smiled softly in appreciation and sat next to him.

After a few minutes of sitting in silence and feeding the birds Marco broke the silence "I'm sorry about everything that happened to your daughter. And that we couldn't do anything to help her or bring her back." Marco said not looking at her. Eclipsa blinked at his words but waved her hands "No no, its fine you have nothing to apologize for. It has just-" Marco cut her off. "No it is my fault maybe if I had magic or powers than I could have helped stop Mina and maybe bring your daughter back to the castle. Maybe Star wouldn't feel so helpless! I can't stand when she is like this!" Marco stopped when he realized what he was saying a bit of pink dusted his cheeks he sighed and looked at the ground away from Eclipsa.

Eclipsa stared at him for a second then smiled a little. "This isn't just about the Monster Bash is it? You felt helpless to be of any assistance to Star and her suffering makes you mad because you care for her so deeply. And you feel as if Tim-" "Tom" Marco corrected. "-has taken your place." Eclipsa finished her sentence as if she did not hear his interruption. Marco raised a hand to speak but Eclipsa continued. "You know she usually talks about this 'Earth' boy more than her boyfriend. AND talks about how amazing and thoughtful her squire is for helping her with her princess duties, organizing her work so she can have some free time, supporting her cause for monster rights. She really admires and cares for you, do you realize this?" Eclipsa said looking back at Marco to see his face as red as a tomato.

He looked back at her with a grateful look "Thank you. I needed that." She smiled "Anytime. And do try and visit if you can, it tends to get boring around here, you and Star are the most interesting people in the castle. And if you hear anything about my daughter please?" He nodded and replied "Okay. And I am beginning to believe the whole 'Queen of Darkness' title is a bit exaggerated and biased."

"Actually that is pretty close. Its the evil part that is exaggerated." Eclipsa corrected which seemed to make sense to Marco. He then decided to go get something to eat. "What a nice young lad. Oh, to be young and in love again." Eclipsa said to herself tossing some bird seed on the ground reliving some memories.

In the Dining Hall

It was time for dinner and when Marco showed up he was surprised to see Star (who is wearing the clothes she got at the start of season 3) and Tom sitting next to each other laughing about something. With Queen Moon sitting beside Star at the end of the long table and River sitting on the left of Moon/across from Star. Ponyhead was floating next to River with Janna and Kelly further down the table. Marco immediately thought back to the Soulrise and the Monster Bash and how close they acted which made his chest ache but hid it well. Star then noticed his presence.

"Oh there you are Marco. I was wondering where you were." Star said making everyone at the table look Marco's way. Tom waved him over "Got a seat right here man. We only started eating a while a go."

Marco swallowed the lump in his throat. Tom was still his close friend after all. He fist bumped Tom and sat on Tom's right while Star was on Tom's left. He smiled at his demon friend "Not that it isn't good to see you Tom, but what are you doing here?" Marco asked "Oh Star invited me after our date to the Amethyst Arcade." Marco simply nodded "So what is everyone talking about anyway?"

"We were just talking about the Royalty Dance that takes place in a week. Its were all the royalty from Mewni, other kindoms, and nobles show up for a yearly party. Its to keep up appearances, make treaties, mingle and such." Moon explained at the end of the table with River on her left (opposite of Star's seat) munching down less food than usual to say something.

"Squires, knights, and other rich or well known families are allowed as well with invitation or as guests. We usually end off the event with a contest between the knights then a dance." River threw in.

Marco nodded and Star looked at him "Yeah and since you're my squire you can come and I'm inviting a few friends as guests to have more fun." Star said cheerfully. "But everyone has to wear a dress or suit to the party to keep up appearances." Moon reminded.

"I have a suit that I keep in top condition so it shouldn't be a problem for me." Marco said eating his corn. "Hey Star I just remembered can use that 'All Seeing Eye' spell to look for Glossaryck? He is in my room but he is hiding for some reason." Marco asked. "Sure." Star said casually pulling out her wand, closing her eyes, and standing up out of her chair.

"I summon the all seeing eye

To tear a hole into the sky"

Her hearts began to glow a white color mid-chant.

"Reveal to me that which is hidden

Unvale to me what is forbidden."

She finished opening her eyes and the crystal turned into a glowing green slitted dragon eye. (A/N her mom hasn't read Eclipsa's chapter and Star doesn't seem to be affected by the dark spells she has cast before so the other magic users have no idea about this spell)

Meanwhile in another galaxy Gaster's Laboratory

"So this is the portal that takes you to the au's that's also what the missions you go on are?" Asked Toriel. Sans shrugged "Yeah basically, but they are not ALL pleasant. There are some seriously messed up and/or evil versions of me and everyone else. Some haunt my dreams to this day." He explained shivering at the thought of some of the other 'hims' and others.

"Like who?" Undyne asked curiously. Sans covered PAP's ears and she covered Mettaton's. "Well there is Horrortale Sans. He has a chunk of his head missing which constantly bleeds you could thank that worlds Undyne for that, always has his blood red power eye glowing , hunts down and eats any humans in the Underground and sometimes monsters due to the food shortage, and is one of the fastest versions of me. I blinked and next thing I know I'm pinned to a tree my arm bleeding with an axe pressed into it with him just smiling evilly at me. And he is not even the worst one or in the top 10!" He said with his irises vanishing due to his dark thoughts.

Everyone was quiet and a little horrified after he explained that. Toriel also remembered fixing up the exact injury Sans mentioned. Asgore coughed into his hand. "Um, so about the mission?" He asked trying to change the subject. "Well we are traveling to a safer au for a demonstration in front of the royals and other political figures. Speaking of which, come on this in the next room." Sans explained leading them through a set of automatic double doors.

On the inside was a large circle room and at the center was an oval shaped device attached to a computer with strange symbols instead of words while connected to a large generator with flashing lights and grey liquid inside of cylinders hooked up to said generator. There is thick glass upwards set up with rows of seats behind it filled with Asgores parents, Undyne's father, Toriel's parents, etc.

Gaster is the royal scientist and father of Sans and Papyrus. He is 34 years old. He is 7'5" pretty tall. He has the same hair and eyes as Sans but his hair is a little longer. His attire consists of reading glasses, a black sweater, black snow boots, black dress pants, and a long white lab coat with extra pockets. He also has holes in his hands for some reason.

Gaster was standing in front of the computer speaking a strange language and hands that confused everyone except Sans who responded casually. "Yeah, but I'd say we are fashionably late. A pretty bonerific entrance by us." Gaster turned around with an unamused look on his face and spoke the same language again except seemingly more agitated. " Hey! That dodgeball thing doesn't count." Sans said sounding like it was more of a question. While Gaster facepalmed. This continued to confuse everyone furthermore then Sans added "Okay fine. Dodgeball does count, but 'I' wasn't the one playing this time."

"Anyway the mission?" Sans changed the subject reminding everyone of why they are here.

Gaster then activated the portal which let off a blue swirling glow and set it for Dancetale. "Everyone get ready." He said going back to English. Suddenly the portal changed to rippling purple with intangible flames coming from the outer edges. Alarms went off and the doors locked shut stopping anyone from getting in to get hurt and from leaving.

"The portal is overloading! An unknown outside source of magic is interrupting the destination and pulling things in!" Gaster shouted holding on to a metal pipe on the wall. Suddenly Alphys, Mettaton, and Asgore got sucked in. Undyne , Papyrus, Gorgette, Grillby, Frisk, Chara, and Toriel followed after trying to save the ones who fell in. "No!" Sans shouted and fell in after his friends after losing the grip of Gaster's hand and flying into the vortex. Which abruptly closed afterwards.

Everyone was to shocked and in despair at the loss of their children, but Gaster had already started to work on getting them back.

The other galaxy at Butterfly Castle

Suddenly Star's All Seeing Eye spell began to shift into a purple ripple pattern vortex which blew out a group of mostly teens and some younger kids. Some teens strangely resembled monster traits. The others looked pretty ordinary. The guards rushed over and pointed their swords, spears, and axes at the children just as the vortex closed.

The older looking male teen with white hair stood up and looked around. He then spoke. "Well I don't find this situation is very humerus." He chuckled. There were many groans and a couple pained laughs in the pile of children/teens.

Marco spoke the question on everyone's mind. "What just happened?"

End chapter