Hey guys so I was inspired to start up a new fanfic after reading something from another author(I cannot remember the authors name Very Sorry!) Anyways, as for the other fanfic, I am very sorry for making you guys wait so long I am still currently hitting a writers block with that fanfic at the moment, just give me a couple more weeks maybe, and I promise I will get the next chapter uploaded as soon as I can! Thank you very much and I hope you enjoy this new fanfic!

Chapter 1: Underswap.

Sans POV

Sans groaned internally, feeling a splitting headache in his skull, he felt like it would shatter, but that lasted only a moment before the pain was gone…along with everything else. His eye sockets snapped open for a second, only to be blinded by light. He shut them again, tightly, unable to process what was happening. He felt weightless, for a moment, before suddenly, all the light was gone, and he felt himself being pulled by gravity again. With a yelp, he fell onto soft, cold and wet ground. He waited for a moment, before opening his left eye. When he realized the light was no longer there and blinding him, he opened his other socket as well, and looked around. He was…outside? He was. The lights in his eye sockets skimmed everywhere, seeing the white snow covering all of Snowdin. He raised a boney brow, confused.

'But…it was just night time…I was just in my bed…" Sans pondered on for a moment, questioning what just happened, until he heard someone call his name, someone he recognized immediately.

"Papyrus?" Sans called out, and he looked up. Papyrus was, in fact, running towards him, but something was definitely wrong.

This couldn't be Papyrus…though he looked and sounded exactly the same, it wasn't him. This…skeleton, all the while had the same facial features, wore a baggy, orange sweatshirt, and short but oversized pants. He wore socks with slippers, too, which shocked Sans a lot, since that was his style. But what really got his attention was the cigarette that hung from his jaw. Sans stared with wide eyes as the Papyrus imposter came running over, his expression showing tiredness and worry.

"Sans! Oh thank Asgore I was able to get you here!" Sans quickly felt his soul pace when this monster reached him and spoke. He teleported a couple feet away, now in a standing position. His eye sockets wet hollow, and he glared at the imposter of his brother, his smile showed anger, confusion, and nervousness.

"Hold up there, buddy," Sans stated, his hands shoving in his pocket unconsciously. "First off, who are you, how do you know me, and how did I suddenly get into the middle of town?" The laid back like Papyrus had seemed to tense for a moment, before relaxing a bit and giving him an uneasy smile.

"Heh, I kind of thought you'd be confused," Sans frowned at how much he sounded just like Papyrus. "I-uh. I brought you here because I need help…someone took my Sans."

Sudden realization hit Sans hard in the face. He had read about this so many times, but he never believed it to be real…but now all the evidence stood in front of him. As he stared, the Papyrus started to give another uneasy chuckle.

"Where…where are we?" Sans finally asked after taking another minute to process what he had just heard. Papyrus smiled a bit.

"Underswap," He answered, and let his smile fall quickly. "Look, I really don't have much time to explain all of this. So we can talk after we rescue my Sans." Sans had to take another moment before nodding, but then had to ask one more question.

"How did you get me here?" He asked. Papyrus sent him another quick smile.

"You weren't the only one with a machine." He said. "Now common I was able to get you here, now we have to gather others...we'll need all the help we can get," He said before grabbing onto Sans' sleeve and teleporting them to Papyrus' home, right into the living room. Sans glanced around a bit. Everything looked similar, but some stuff was different. Like their rooms. Their rooms have switched around, where Papyrus' room was in his home, was a clean door, while where Sans would see his bedroom door was covered in different signs. It was only now when Sans understood this place. It was Under'swap', so everything must have swapped, including everyone's personalities.

"So…can you maybe tell me what's going on 'round here?" Sans spoke up, looking around as he followed Papyrus outside to the shed. Papyrus sighed a bit, and Sans could hear the sadness in it.

"Well…my Sans and I…we were just going to Undyne's home to see if she could hook us up with some more taco shells…heh, we had run out.." He smiled slightly at the thought before frowning again and sighing. "I should've noticed something was wrong from the start…when we got there, there was almost no one out there, it was so quiet. When we got to Undyne's house, she wasn't there, so we decided to check the labs…y'know, cause she's always likes to hang out with Alph…neither of the were there either. Then, I-uh, thought I heard something in the labs. I told Sans to wait outside while I checked it out. I should've taken him with me…or paid more attention, cause the next thing I knew, something attacked me and took Sans. I caught a glance of something…a glitch, and I think some blue strings, and I knew who it was...I've read up on this guy before, and that got me to worry and bring you here."

Sans raised a brow, but frowned. "Who was it?" He questioned, almost sounding nervous. Papyrus sighed, and looked down at him.

"Another you…" he muttered. "This Sans…he's known as Error Sans. A glitch, I would say, but that's what he calls us. He's a murderer, killing off so many other universes and timelines…that's why everybody in the timeline was missing. I should have seen it from the start…but it was too late. When I found him, he was already trying to take my Sans. So I tried to fight him off…but in the end he was too strong. For some reason, he spared me…and took my brother. Now I need to find him and get him back…but I can't beat him alone...so I need your help."

Sans was shocked to say the least. He had heard of Errortale before, but had never believed any of it was real. But now he had no choice but to believe. And he knew that if he took Underswap Sans, it wasn't for any good reason, and they'd only have a certain amount of time before they could get him back.

With a small nod, Sans finally responded. "Alright…I want to help you get your Sans back, but…I don't think the two of us could do it alone…we would need a lot more help."

Papyrus looked back and gave him a bit of a smile. "I knew that already. You're just the first person I could get so far." He stated before opening the door to the shed. Sans took a peek inside and saw the same busted up machine that was sitting in his own shed, only this one looked more battered and used, like someone tried to fix it recently and it broke down again. With a small frown, Sans followed Papyrus inside, and walked to the machine to get a better look. Wires stuck out in various places, and nuts and bolts were scattered around the ground, along with a few other metal pieces.

"I tried to make it so that I could bring other universes to my own, but it apparently took more power and magic than I thought it would to do that. It was only able to get you here before it broke down." Sans looked to Papyrus when he explained it. "So…we have to try and make a different way, because it almost caused a blackout in Snowdin. We need to be able to use less magic for this."

Understanding, Sans glanced down in thought. That would be hard. Bringing another universe over would take a lot of energy, about as much energy as the town. Though there wasn't many other choices other than….no, that would be extremely dangerous, but no more dangerous than bringing another universe over, Sans guessed. So with a thought in mind, he looked back over to Papyrus.

"What if we brought ourselves to another universe?" He asked aloud for the taller skeleton to hear. Papyrus stopped and stared at Sans for a moment, wide sockets while he stared, before shaking his head slightly. "But…that's dangerous…we could get caught in the void if something messed up," Papyrus said quickly, more serious than ever. Sans frowned at him. "It's about as dangerous as bringing me here. If something happened to the machine before I was able to reach your timeline, I would have been stuck in the void as we speak. It's the same risk. Except this plan would take less energy, and so there would be less of a chance of failure." Papyrus glanced down, looking like he was in deep thought for a moment, which made Sans speak up again. "If you want to save your brother, this is the best and only way." He said, his tone dead serious. Papyrus made a small grunt before nodding. "I guess you're right. Whatever it takes to get my Sans back."

They didn't need much more explaining to do after that. They went directly to work, moving around from the shed to the shop, to the labs, trying to grab any pieces that they could use to fix the machine again. Papyrus worked harder than Sans, though Sans only knew it was because he was the one who worried about Swap Sans the most. Sans would have made a joke about Papyrus' look, but seeing the situation they were in, he knew better than to make jokes at the moment, so he stayed silent as he worked. They looked over blue prints, made corrections, changes and rarely took breaks. It took longer than Papyrus would have wanted, but after almost a full week, their project was almost done.

With a honey bottle by Papyrus' side, and a ketchup bottle by Sans', they stared at the newer looking machine, along with two new pieces. Sans held them up, and he and Papyrus admired the work.

They looked like metal necklaces, but they were thicket, with buttons and wires attached and looping around. With a small nod of satisfaction, Sans looked up at Papyrus with a small smile.

"Alright, it's almost ready. We just need to test it now." Setting their work on the table gently, Sans went to the other side of the shed and dug around, knowing the place inside and out. Though it wasn't exactly his shed, it was pretty damn similar to it, so it was easy to figure out what was where. After some moments of rummaging, Sans pulled out an only looking camera, and opened up the film cartage quickly, satisfied to see there was film to work with. Walking back over, Sans turned on the camera, and put it to video before wrapping one of the wired metal pieces around it.

"Alright. If our theories are correct, we should be able to send the camera to the next timeline, so long as the travel piece doesn't fall off," Sans explained, pressing a couple buttons on the travel piece before stepping back. Papyrus frowned slightly and glanced towards Sans. "What happens if it falls off?" He asked skeptically.

"Well, if it falls off between the travel from universe to universe, then it'll stay lost in the void. If it falls off in the other universe, then it'll get stuck there." Sans explained.

"And, if another monster from another universe touches it?"

"Then that monster goes with it. They'll be able to travel with us as long as they have some contact with the person wearing the travel piece. That's how we'll get the help we need here. Only problem is, when we go, we don't have a backup monster to help us get back if our travel piece malfunctions…" Papyrus' bones seemed to tense slightly at that. "What do you mean?"

"Well, the machine is a backup plan," Sans explained, pointing to the large machine that leaned against the wall. "It's connected to the travel pieces, so if they malfunction, with a press of the button, the machine will bring us back. Only, since right now it's just you and me, no one will be able to man it."

"Why can't just one of us stay in case?" Papyrus asked. Sans only chuckled. "Well, buddy, because not all the other Sans' or Papyrus' are going to be all that friendly if they see a doppelganger of themselves. It's better to have someone with you rather than going alone, y'know? It's safer." Papyrus gave another small grunt, but he knew that Sans was right, so he nodded. "I guess," he muttered. With that, Sans turned away from Papyrus again and looked towards the camera.

"I already have the camera ready. I set in some coordinates to the closest universe to us. I'm not sure what it's called yet, but if this works, we'll be able to catch a glimpse of their timeline. If that works, then we'll be set to go and reach that universe ourselves and bring back whoever we need from there."

With a nod of understanding, they both now watched the camera. Sans stood next to the big machine that stood against the wall, and while praying to Asgore that it would work, pressed a button.

There wasn't much that happened right away. A small buzzing came from the machine and the travel piece. Papyrus automatically became nervous that it wouldn't have worked. But by the next second, there was a small spark that came from the travel piece, and then a bright flash that forced the two skeletons to cover their eyes. By the third second, the blinding light was gone, and when the two skeletons looked back to where the camera was, they saw that it was gone too. They looked to each other, and Sans gave a smile. "So give it a few moments to record what's going on wherever it is, and then we'll bring it back." He stated.

And that's exactly what they did. They let the device record for a minute, before Sans went to the machine and quickly pressed another button. Like before, there was no sign of anything, other than a slight hum from the large machine, but right after that, there was a blinding flash, and the camera was right back to where it was before. Papyrus was the first to take the camera into his hands, and flipped open the small screen that was hooked to it. He turned off the recording as Sans walked over, and played back what was filmed.

They had to skip they're explanation, but after that part, they watched as there was a bright light that caused the cameras lens to go out of focus. But then the light was gone, and while they watched the camera try to refocus the lens, they heard distant voices. They sounded like angered shouts that got closer and closer. When the lens focused, they could see that the camera ended up on the ground, in snow, just like Sans had first turned up. Suddenly, there was a pair of feet. They wore bright red sneakers, and attached to those sneakers were thick, boney legs. The two watched with wide eyes, hoping to see who this person was. They got a glance of a dark red jacket, a red shirt underneath, and a sharp toothed, confused grin right before there was another flash, and then the film ended. They had sent it back before they could catch a look, but they could tell right away whoever it was wasn't from around there. Sans gave a bright smile and looked towards Papyrus, who seemed both shocked and amazed as he continued to stare at the camera.

After a few minutes, they went back to work. Sans had to tweak with the machine a little bit before they got themselves ready for their travel. He reset the coordinates on the machine again, and went back, taking the travel piece off the camera that was eventually set back down on the table. He also grabbed the other travel piece that was laying on the work table before heading back to Papyrus' side and handing him one of the travel pieces. Papyrus took it, and put it on over his head, laying it around his neck like a necklace, then watched as Sans did the same. Sans then pressed a couple buttons on the travel piece around his neck and showed Papyrus exactly what to press to get the coordinates down into his travel piece. With a small nod, Sans walked back over to the large machine.

"Alright, you ready for this?" Sans asked with a raised, boney brow. Papyrus shoved his hands into his bright orange sweatshirt before giving a nod. "As ready as I'll ever be." He responded. With a small nod back, Sans looked back at the machine.

"Alright, see you at the next timeline then," Sans said before pressing the button on the machine. There was nothing more than a faint hum at first, but suddenly there was a blinding light, and a skull crushing pressure like feeling inside of Sans' head, which made him black out before he could see what had happened.