A scene of Endsville two weeks into the future shows a dystopian world ruled by the "Lord of Horror", who wields the all-powerful artifact known as "Horror's Hand". At the same time, two robotic replicas of Billy and Mandy are sent into the past, to stop the real Billy and Mandy from interfering with the current events.orror's Hand to rule the world.

On a rainy day, giant spiders appear in Billy and Mandy's school and start kidnapping the children one by one. Grim presumes this is somehow related to his past, but does not figure it out until he receives a message saying that Velma, the Spider Queen, an old good friend from high school, is responsible for it. Meanwhile, Billy meets with Jeff the Spider, who informs him that he is precisely marrying Velma. After trying to recover a talking carton of chocolate milk from Jeff, Billy and Jeff get into a fight, and Jeff looks angrier than ever before.

Billy, Irwin and Mandy go trick-or-treating on Halloween, and an evil marshmallow bunny attacks children with chocolate beasts.

While Billy's Dad is underwear shopping, Billy wears his dad's lucky pants, and accidently rips them with Grim's scythe. He calls Ed, Edd n Eddy, and they recommend Kids Next Door for charity.

Billy looks into Grim's trunk and sees a monster and names it Myron. But when Billy brings Myron outside to his backyard, he gets eaten.

Billy's Dad forgot to buy Billy's present for his birthday again! Everytime Billy's Dad buys a present for Billy, he will get distracted by a "Rocket" Kiddie Ride. He found a way to give Billy a present that will be "The greatest gift ever, made by the hands of Man" Billy's Dad gave Billy a macaroni bike, but the macaroni Billy's Dad used are the ones supposed to be used for the macaroni salad. The short ends with everyone eating macaroni salad while Grim vomits upon learning the truth of the secret of the macaroni salad (Motor Oil).

Grim decides to make a cake for Billy's birthday, but he and Mandy end up making a Devil's Food cake that comes alive and began wrecking the kitchen. The cake hops on Grim's face but Mandy smashes it and splatters it all over the kitchen. Grim and Mandy give Billy a cake covered kitchen, much to Billy's delight.

Irwin finishes wrapping Billy's present and buys a huge present for Mandy as well. He decides it is not big enough so his dad decides to teach him how to dance. Irwin writes her a rap and Irwin's dad ends up teaching him how to work out instead of dancing. Irwin shows his moves to Mandy, but Mandy rejects him; Irwin also gets a wedgie from Sperg.

Dracula was heading for the bingo hall when he ran into Pud'n who was on his way to Billy's party. Dracula was insulted he was not invited to the party and decides to crash it. Harold will not let him in and accidentally calls him old. Dracula starts dancing and breaks all his bones, much to Harold's disgust. Harold lets him in so he will stop.

Billy blows out the candles off his cake and Dracula turns to leave, but Billy stops him and forces him to stay for games. They play Pictionary as he draws Abraham Lincoln but no one guesses it. Everyone turns to leave but Billy stops him and forces them to party all night. Billy decides to get a pinata but the stores are closed so Billy forces them to stay all night until Grim and the others decide to use Billy as a piñata.

Irwin has a dream sequence of taking Mandy out for the time of her life.

Dracula tries to help Irwin win over Mandy.

Irwin's grandmother, Tanya, embarrasses Irwin in an elevator ride with Mandy.

Irwin's future grandchild travels back in time to motivate modern-day Irwin to give Mandy a box of chocolates, but bully Sperg stands in the way.

Grim and Dracula go on a double date.

Irwin tries to win over Mandy.

Grim has difficulty teaching Billy how to tie his shoes.

Irwin wants to take Mandy out to dinner, and schemes to get money from the tooth fairy to pay for it.

Billy battles his messy room.

Dracula participates in his senior home's self-defense course by role-playing as a "victim."

Billy builds a snowman that comes to life.

Irwin wants to impress Mandy and goes to Grim for help.

When the gang frees Thromnambular, the wish-granting skull, from a lamp, Grim and Mandy bicker over who gets to make the first wish.

When the Grim Reaper tries to take Billy's pet hamster, Mandy and Billy make a deal to save his life. So the Grim Reaper challenges the kids to a limbo competition.

The day before Christmas, Billy, Mandy and Grim go to the shopping mall, where Mandy complains that Santa Claus is just an invention from corporations. Grim assures Mandy that Santa is real, and they even went to college together. They decide to travel to the North Pole and meet Santa, but when they arrive Mrs. Claus tells them that Santa Claus has been transformed into a vicious vampire.