He kept sitting on a sofa, in his room, a room with excellent memories, he still kept the half sock in the corner of the room where Papyrus left letters telling him to remove the socks, he gave a sad laugh, his brother did not know but he did it just to see if Papyrus still cared, if he still cared about him, his sloppy style was always common for the monsters, believing he was just a lazy one, but nobody cared, they liked the bad jokes and of the fake smile he always had, a smile to hide everything that was going on in his mind, he slowly put his hand on his face, while his eye shone, the child, that demon did it, he really managed to destroy everything he cared about, his kind actions hiding a sociopath, he pressed his face in anger, he had to kill his own friends because of that bastard, he had to kill his own family....
He had become a monster, Papyrus tried to kill him, but he could still see goodness in him, even so, he would never understand, his innocence was used against himself, and Sans....
Sans didn't even notice how he himself was used....
And when he tried to fix everything, what happened? He succeeded, he managed to take the human soul for him, but at what cost?
He could be powerful now, but now, he didn't know how to rebuild his world, he didn't know how to use the Overwrite button, because of that, his world was now empty, with nothing and nobody, and with one of the brats accompanying him all the time, he tolerated that asshole for a while, but he knew he wasn’t trustworthy, even though he knew Ink and saw a possible friend, he was very foolish, and he didn’t want to help him fix the damage done, shit, he didn’t even tried!
It irritated him deeply, that bastard of paint just tried to give him moral lessons about friendship and leaving the past behind.
He says this because it is easy for him, the guardian of the Multiverse not only works alone but the only thing he cares about is himself, he is a hypocrite who says he brings sympathy when HE DOESN'T KNOW HOW LOVE!
Alone he had time to think, he screamed, he cried, he sobbed, he cursed.
He didn’t know what to do, he was desperate.
So Nightmare showed up, he says that all my negative emotions caught his attention, saying that he "never saw any Sans with so many negative emotions", he laughed at my problems, I would have killed him, if I hadn't heard him, he felt that by my "tasty" feelings he would give me a chance to restart my Universe, this offer was too good to pass, so I listened to him, I would have to make everyone suffer in all the universes he took me to, I would have to create as many negative feelings as I could.
Sadness, anger, hopelessness or whatever we prefer not to feel.
I would have to sell my soul, but I accepted, all to correct my past mistakes and rebuild my universe little by little.
If regret killed, I would have been dead for a long time, but I didn't stop, and the worst, I started to like it, with every universe I visited, I made people suffer, I killed their loved ones in front of them, tortured some just for the sake of it, I slaughtered entire villages, and destroyed entire cities, and each time I became better, each time, I hesitated less, and each time, I felt more alive with each stab I took, each house I burned down, I felt more pleasure.
I knew I was going crazy, that I would lose someday, but for my home, for Papyrus, it doesn't matter, it is necessary.
And better, I got rid of the idiot in my head, I got it after a few more services for Nightmare, he removed Chara from my soul, now there is only me, and me only
With each Universe that I caused despair, I managed to rebuild my universe more and more, Snowdin is almost completely recreated, I just need a few more trips, some more massacres, and I will be able to complete the holes.
He thought as he stretched out on the couch, he slowly got up and walked around the room, she was not the same as he remembered, but it was good enough, he slowly opened the door and walked down the frozen street of the corrupted Snowdin, a black covered creature of a dark goo he kept looking at the half-formed Christmas tree, keeping Sans trademark smile, while his tentacles slowly speculated the tree.

"You know, i never understand you Cross...."

Nightmare said with his back to Cross, that was arms crossed with a raised "eyebrow" at him

"Why try to recreate something? Why not make the universe your image? Or something you think is better?"

Nightmare looked back, keeping his back to Cross, to see his expression as he answered, Cross maintained his posture, and slowly maintained quiet, looking up to the unfinished tree.

"I just.... Want things go back as they were..... Without a human to meddle in our lives, to be able to live in peace..... and to correct my mistakes...."

He would say while his face would keep his expression neutral, he knew that explaining to Nightmare the good things about having a family were useless, Nightmare was a diabolical being who only cared for himself and fed on the disgrace of others, but he didn't want to stay on his bad side, so he answered sincerely.

"Thats patetic, even now you have all the cards to make whatever you wish, and you just toss them aside."

Nightmare said looking at him with one mocking smile while Cross maintained one neutral expression.

"But I don't care, if I get negative feelings and that you keep part of your agreement, I'm satisfied"

Cross walked slowly and stopped beside Nightmare, turning to face him, the shadow creature kept facing the Tree, but with its eyes fixed on its counterpart

"If you came, you obviously want something, what should I do?"

Nightmare just smiled even more at the deduction of his companion

"Smart boy, yes i have another job for you, knowing your specialties, I knew you were the right Monster for the job"

Ignoring the nickname given to him, Cross nodded, Keeping his smile, Nightmare teleported them, both disappearing from Corrupted Snowdin.

Both then appeared on top of a hill, looking at a small village, in which one could see many... Horses?
Yes, Anthropomorphic Horses.....
All with diffrent colours, sizes and all with tattos on their flanks....
What else? Will sunshine come out of their asses aswell?
Monsters came in all types, shapes and colors, but he had never seen anything like this...
Nightmare was leaning back against a tree looking at Cross who was looking around

"You know the deal, kill, but not everyone you come across, make them suffer, torture as many as you can, make more than just physical pain."

Cross 'crossed' his arms (Batum-tss) and nodded, while looking at that colorful and happy village, it was annoying see them, jesus, look at them, acting like everything is wonderful, like nothing is important, like the world is a party, where do they think they live? a fairy tale? he looked at Nightmare.

"I understand my service, and it will be done, however, what kind of alternative universe is this? I thought it was just our alternative versions, not... this...."

Cross made a sign with his hand pointing to the village, Nightmare looked and disgusted when he hit his eyes they came into contact where Cross pointed.

"The Multiverse is much wider than you think idiot! It is not only alternative versions of our worlds, but also alternative versions of thousands of others, Dream and Ink protect a tiny part of the multiverse if you were able to see the size of it all, you would know we are like a grain of sand in one entire desert! Universes are always created and destroyed, is a constant struggle between creation and destruction, there's all kinds of universes that you can even imagine! believe me, I saw one were humanity governed the entire galaxy, another were Monsterkind never even existed, another were there was teddybears that spread love, and this is one of them, his positive feelings are so powerful that they reach our part of the multiverse with its 'harmony', it's annoying, it's disgusting, that's why I want to that you get rid of it, hell, destroy everything if you want, just getting rid of all that positive energy is going to be a huge favor that you will do to me, here it doesn't have a balance like other universes, here, in the smallest of chances, instead whether corruption reigns, or is in constant confrontation with creation, here, Harmony is dominant, and 'happiness' and 'prosperity' are everyday things in this shit."

Cross was surprised even though he didn't show, by Nightmare's explanation / ranting, he was not someone you would expect to lose patience easily, and he understood a little more about the Multiverse, it was something really vast and difficult to understand, but he nodded to Nightmare confirming, the former just smiled, disappeared, teleported away, Cross would look at the village and summon his giant sword and rest it on his shoulder, and slowly walk to the small village, he had a job to do

Author's Note

Finally! I had enough inspiration to do this chapter! I love Underverse and the concept of transportation in the multiverse he is looking to rebuild his universe, now he is going to cause chaos in Equestria! Did I do something wrong? Orthographic error? ideas? I am all ears! Criticize me! Thank you and peace!