WARNING: This first chapter contains a pretty...graphic sans. If that kind of stuff disturbs you, I recommend you skip to the second half of the chapter (I'll let you know when you can read again). I'll try to provide a summary of the beginning for those that skipped. This should be the only chapter with a graphic description, but if any of the other ones get too graphic, I will put a warning similar to this one at the beginning of that chapter. Now, on with the fic!

The Insane Sans stood still for a moment. Somehow, he had just encountered another version of himself. Could this mean...? He tried hard to think, which was difficult due to his insanity. Finally, he reached out, and appeared in another Judgement Hall. It looked very similar to the one from his universe, but he noticed something strange. Instead of there being another Sans, there was a human in a green jacket. They seemed just as confused as he was.

"Sans?" asked the human. They were slightly taken aback by the blood-stained clothes covering the skeleton. It was then they noticed the skull they were holding. "I don't who you are, but Sans would never kill his brother."

"Heh heh heh, who said I wasn't Sans. I am very much Sans, just not the one you know..." growled Insane Sans.

"Well then, greetings. I am Chara. It's a beautiful day outside. Birds are-" Sans interrupted Chara as he rushed at them with a sharp bone in hand. Chara barely dodged, fear evident in their eyes. "Alright then, now I know you aren't the Sans I know." They brought up their knife to block Sans's attack. In return, he brought up his fist and punched the human in the gut. This sent Chara flying against the wall, where they sank to the floor in a daze. They looked up just in time to see a bone fly into their face before everything went dark.

The Insane Sans grinned as he looked down at the bloody mess of the human. He looked down at the skull of his brother, which he carried with him everywhere he went.

"Well, Papyrus, looks like we're going to have lots of FUN!" Insanity exited the Judgement Hall, laughing like a mad skeleton as he went off on his next killing spree.

(Ok, if you wanted to skip the gory part, you can read now)

Ink jumped back from his portal. He had been watching the Storyshift universe from within the Doodle Sphere. It was in the middle of a pacifist route, and he had wanted to watch SS!Chara judge the human. However, what he had seen was something else entirely.

"Dream!" he called out. Dream teleported there almost instantly.

"You called?" he said.

"We have a problem..." said Ink. He explained what he had just witnessed, as Dream gasped in horror. "Do you have any idea who this Sans was?"

"I'm afraid I do. I've heard my brother talk about a Sans that fits your description. He is Insanity!Sans, a Sans that was injected with determination and went insane, resulting in one of the bloodiest genocides in the entire multiverse. Unfortunately, he appears to have figured out how to travel across universes."

"Honestly, he seems quite unpredictable. Pretty interesting if you ask me," noted Ink.

"Ink, I understand you have little regard for what actually happens in the multiverse. But if this Sans is allowed to roam free, he will destroy everything and become unstoppable! As you said, he is very unpredictable and very dangerous!"

"Fine, then what do we do?" asked Ink.

"We won't be able to stop him on our own. As much as I hate to admit it, we're going to need to get some more help. I'm going to try to talk to my brother to see if he is willing to help. You need to go and find the most powerful people across the multiverse and bring them here. Can you do that? Ink?" Dream turned to find Ink drawing a picture. "INK!"

"Oh, yeah, I can do that. Um, what am I doing?" asked Ink. Dream sighed.

"Ink, for once I need you to focus. Go find people that can help us fight Insanity. And don't bring Blueberry. As fun as it would be to see him again, I'm not risking his life against a foe as powerful and unpredictable as Insanity."

"Right, I'm on it. Oh boy, this is exciting!" Ink suddenly threw up black ink. Dream didn't even flinch. He had gotten used to the symptoms of Ink's excitement. He watched Ink paint a portal to some random universe, while Dream went off to search for his brother.

Author's note: Ok, here we go. First off, for those of you that skipped the beginning, there is a new threat to the AUs known as Insanity!Sans (I will provide source links for all AUs introduced in each chapter). We start off right after Mirrored Insanity, a fight between Insanity and Dust Sans. After the fight, Insanity realizes that he can travel between AUs. His first stop is Storyshift, where he encounters SS!Chara kills them. And that's all that happened in the first half.

Now, time to discuss my plans. This fic will be a bit different from my previous ones, as it will focus on the Undertale multiverse. However, I want to try to include some lesser known AUs, hence why Error is not the main villain. Plus, I felt like it would be a bit too cliché if this was just another Ink vs Error story. I also want to include some non-Sans characters, but that might be difficult as almost 90% of the fandom is Sans. So, if you have any ideas as to who I could use, feel free to let me know. I'll do some research and see if I can make them work. There is also something else I want to clarify. AUs that were not specifically made for exploring the universe will have little to no bearing on the plot. There might be some exceptions, but for the most part AUs such as Underswap, Underfell, etc. might make small cameos, but they won't have much influence on the main plot. I'm also not including X-Tale/Underverse at all because I don't want to do something that will go against the plan of the creator.

One final thing, the upload schedule for this fic might be a little sporadic. I have to admit, I have a very vague idea of what I want to do. I didn't have a good idea for the title! (If you have a better idea please tell me. I will give you the biggest shout out if I end up using it lol). Anyway, please let me know what you think, and I will see you in the next chapter.

Sources (Please note that some of these links have images that might be disturbing to some readers. If this is the case I will put a * next to it so you know to visit at your own risk):

*Insanity!Sans Fanon Wiki Page: wiki/Insanity!Sans

*Mirrored Insanity: MIRRORED INSANITY Remade [Complete Music Video] (ReveX Remix) 5K Subs Special (Read Desc For Info)

Ink Sans Fanon Wiki Page: wiki/Sans/Inktale

Dream Sans Fanon Wiki Page: wiki/Sans/Dreamtale

Storyshift Fanon Wiki Page (I would link directly to the comic but I feel like the wiki will be more informative): wiki/Storyshift