LJ, Zofia, and their friends come to celebrate Halloween with Billy and Mandy. However, not all is well when Grim tells them the story about a prankster known as Jack O. Lantern who lived in ancient times, causing tricks for people. Due to Billy's stupidity, he comes back and takes Grim's scythe to make it Halloween night forever so he can conquer the world.

As they settle into married life, Nergal decides to reveal to Sis the story of how he grew up and how he came to be banished from the Underworld. In the meantime, the powers that be threaten their future ... a future Sis is keeping a secret for now.

They've faced down an evil marshmallow bunny, squid attackers from the underworld, aSTRoVaMPiReS, and spiders. They've grown close...er. They're accepted as Earth's heroes...kind of. But now, Underfist faces its greatest challenge yet...the judicial system!

Mandy finds out that she has a voice of a angel.

Puro Hueso esta involucrado en una extraña profecía que amenaza tanto el mundo de los mortales como al inframundo, el problema es que Mandy y su primer amor tienen que ver con esto. Por ello de la forma mas indiscreta intentaran encontrar a ese primer amor de la rubia para ver de que forma detienen todo, si es que pueden. (Aviso GrimxMandy)

Grim found out that Mandy is dancing.

LJ and Zofia start going to school with Billy and Mandy, but luckily, their friends Dib, Gaz, Nergal Jr, Kimberly, Chrissy, and even Akito and Estelle will be going with them. It's not a very good first day of class though since there's a spider infestation, and it turns out that the school is going to be held for the Spider Queen for her revenge against the Grim Reaper.

Billy and Mandy are teenagers when they accidentally got transport into the Underworld where they must find a way out before the Boogey Man and Nergel will take over Endsville.

But no matter how hard I try, work, or plan, I will never be able to own an ounce of the happiness Billy contains in his soul. It is self administered. Personal. And illusive. And so, if I cannot own happiness, I will have the next best thing. [Complete]

Based on the SpongeBob episode "Rock-a-Bye Bi-Valve": Billy and Mandy are older now, and find an abandoned child. With no one to take care of him, Billy and Mandy decide to raise him as their own. But with Billy constantly working and never giving Mandy her break, tempers start flaring around the odd couple. This fanfiction is only BillyxMandy if you want it to be.

A followup on "The Secret Snake Club." Irwin is released from jail and meets up with a certain macrame club member. A CarolxIrwin oneshot. Request fic.

In this story, Mandy decides to give a very special Halloween treat to someone who helped her on her first Halloween.

Only the journal entries can show the true killer. Billy, Irwin, Mindy, Nergal. . . . . Oh, who could it be if its even one of them.

After facing down the aSTRoVaMPiReS, Underfist learns of an all-new threat seeking to take over the world–and this new threat is led by Velma Green! Will Underfist be able to stop the Spider Queen? Will Fred Fredburger eat nachos and frozen yogurt? Will there be cobwebs everywhere? Find out the answers to these questions and more in Underfist: Return of the Spider Queen!

An extended ending to "The Greatest Love Story Ever Told." In which Nergal Jr. apologizes to a certain girl.

The long-awaited sequel to Underfist: Halloween Bash...is never coming out. Why? Because Cartoon Network didn't renew Maxwell Atoms's contract a decade ago. Instead, there's this: a fanfiction attempting to continue the story of Underfist. Join Irwin, Fred, Hoss, Jeff, and Skarr as they take on their biggest challenge yet: the aSTRoVaMPiReS!

Mandy's archenemy Mindy is at it again, and this time she makes a dare with Mandy like no other before. Now, Mandy has to find a boyfriend in a week before Mindy does, otherwise she'll have to be the read headed girl's slave. Little does Mandy know, what comes out of it is an experience that will change her life forever. BillyXMandy. T now for language, M later for lemons.

Billy and Mandy never liked each other but, they also never, didn't like each other.

The story of how Mandy learns how to smile without ending the world.

Chael and his childhood maiden friend, Belle, visit his father castle. Not long, friends from different dimension comes along as well, to visit the castle and them. [MultiCrossover]

One day, Billy and Mandy was fighting for Grim scythe when all of a suddenly, they were put under a curse. The curse cannot be undone, to what Grim had putted. The scythe been going crazy since Grim execution day. The day of that incident...

someone is depressed - future fic

Based off the fanfic 'Flapjack and His Random Adventure.' Billy, Mandy, and Grim have a great time on a wonderful weekend day. But things go crazy when they go doing random things. Rated T for swearing, nudity, and of course randomness.

A trip to the Underworld Forest leads to unexpected feelings. A GrimxVelma oneshot.

After Mandy is put on house arrest, Grim becomes a torch singer. A parody of "Mind Over Murder." Rated T for suggestiveness throughout and one bad word. Also for a middle finger. Sorry if you get offended. Also, if anyone is confused, they are teens in this.