A Multiverse Phenomenon drags Nightmare to a place that should be unreachable. Yet it changes the course of this Multiverse irrevocably.

Papyrus is ready to start his first day as a royal sentry, but life has a way of upending plans. After messing with his brother's time machine, Papyrus finds himself 10 years in the future, and what a terrible future it is! [Horrortale AU]

A pregnant 18 year old fell into the underground after running away from her fiancé, Toriel takes her in. Romance blossoms between her and someone else in the underground. But something is up, Siena, Frisk, and Sans try to figure out what it is. Trigger Warning: Mentions of SA, Slurs, and Dark Themes.

This is a sequel to my old story, Integritale, which you will find in my profile. I don't know if this could be considered an AU to the Undertale Universe, since I did add a lot of stuff, but still tried to adhere to the canon as much as possible. In any case, please, enjoy! Any feedback is welcome!

It's only thanks to you that I could change from a sadistic ogre to what I am now. I feel alive for the first time. I can't thank you enough, but I can write down my story. - This story follows Frisk and Chara from a genocide run to a truly happy ending!

The butterfly effect is known as "a property of chaotic systems by which small changes in initial conditions can lead to large-scale and unpredictable variation in the future state of the system." The smallest of changes make the largest of impacts. So… What if when Angel and Frisk fell… they fell into different locations? Squeal "One World, Two Souls", and "One World, Many Souls".

Toriel tries a more adult option to keep Frisk from going into the ruins.

Born into a life of cruel subjugation and confinement, a young child discovers that a different kind of prison might just become her safe haven. But nothing is ever that simple. With a deadline looming and troubles starting to pile up, a new friend with a lazy grin could be just what she needs right now. Multiple AU's. Slow burn. Female Frisk. Contains OC's. Eventual SansxFrisk

"Long ago, two races ruled over Earth: Humans and Monsters." One race feared for their strong souls, the other for their magic, and the mages caught between them feared for both. All silently knew that war would be inevitable. The only thing that mattered was surviving it. One crimson mage understands that well, and is determined to keep herself and those she cares for alive.

You are dropped into the underground world, home to many monsters when a very voluptuous goat mom approaches you and takes you in. There are many mysteries centered around you. It is up to you if you wish to uncover them. This thicc monster lady would like to help, but she wants quite a bit from you. Will you be able to satisfy her overwhelming needs like her husband? Could what yo

A kid falls down a vast chasm into the deep, and is set upon by countless monsters eager to murder whoever falls down and claim their souls. Somehow, this child is the villain in your story.

(THIS IS VERY AU BASED. ASGORE / TORIEL ARE TOGETHER AND ASRIEL IS ALIVE. CW OF ABUSE / CHILD ABUSE, TRAUMA, AND DARK THEMES ARE PRESENT) It's almost been a decade since the war of the humans and the monsters had ended. Centuries of conflict have left the Underground in a state of repair and despair. Although it's going to get a lot more interesting when a soul of Bravery falls.

Sans tries to use a new strategy to save his world from the being that is trying to wipe out all of monsterkind. This backfires tremendously when a human from the real world (that doesn't even know about Undertale) gets transported into his universe. Will this result in friendship, a game of cat and mouse…or the absolute?

"El jugador" ha muerto... Y ahora todos quieren JUGAR. En la peligrosa Ebott City, radica una constante inconformidad por habitar monstruos y humanos en un mismo lugar., desatándose conflictos delictivos que atentan con la vida de los habitantes. Sin importarle las advertencias de su madre, Frisk decide ir a la ciudad y tener su florería junto con su compañero y mejor amigo Flowey

This is just a simple Oneshot that came to my mind after playing Undertale Red and Yellow version 2.0. What can I say? I love this ship. If you like, I can make individual chapters about the 'life' of these two ghosts!

After Frisk's father died when she was eleven and her mother became heartbroken Frisk swore she would never fall in love... until she meets a very punny skeleton named Sans.

Sans is tired of the resets. He decides to do something about it to change things for the better. Everything just sort of goes downhill from there. Created By: AveragePotato

After falling into the Underground, Frisk is found by a young Monster and taken home, where they find friendship and family, and make a new life for themself in the Kingdom of Monsters. But despite the happiness, something lingers in the back of their mind, and soon, they find a way to repay the kindness which they have been shown.

For Monsterkind, the Surface represented freedom. For Frisk, it's a return to some uncomfortable realities. It all began with a simple wish. When that wish faded, Frisk tried to move on. Except, 'moving on' was not so simple. Emerging from the Underground had put them in a worldwide spotlight. From an unknown child, they had become an icon of great value.

Daniel es un chico de 20 años con un gran apego a su cariñosa madre, pero ella contrae una peligrosa enfermedad que le costaría su vida, para poder curarla necesita un ingrediente muy especial. Flores Doradas, Daniel debe partir al Monte Ebott pero caería en un agujero que lo lleva a conocer un nuevo mundo y a una bella mujer cabra, del cual el se enamora perdidamente.

After a tragic accident, a young boy named Vance wakes up in the world of Undertale his favorite game. Reincarnated as a human with magic powers, he finds himself living alongside the monsters he once knew only from his screen. With familiar faces and unexpected adventures around every corner, Vance explores the Underground.OC Harem Fic include characters from Deltarune/ UT Yellow