Billy's pet hamster, Mr. Snuggles, celebrates his 10th birthday, so the Grim Reaper comes for him. However, Mandy, Billy's friend, is reluctant in allowing it, so she proposes a deal to the Grim Reaper: if he beats the kids in a game, he can take the hamster, but if he loses, he will spare the hamster's life and become their "best friend forever". The Grim Reaper transports the kids to limbo, where he challenges them to a game of limbo. Despite his best effort, Grim ends up losing because he is attacked by Mr. Snuggles at Mandy's command.

Billy's pet hamster, Mr. Snuggles, celebrates his 10th birthday, so the Grim Reaper comes for him. However, Mandy, Billy's friend, is reluctant in allowing it, so she proposes a deal to the Grim Reaper: if he beats the kids in a game, he can take the hamster, but if he loses, he will spare the hamster's life and become their "best friend forever". The Grim Reaper transports the kids to limbo, where he challenges them to a game of limbo. Despite his best effort, Grim ends up losing because he is attacked by Mr. Snuggles at Mandy’s command.

Billy's mother, Gladys, first notices Grim in Billy's bed, then in the shower and subsequently starts to get panic surges thinking that Billy is in danger. Meanwhile, Harold, Billy's dad, just thinks that Gladys is imagining things. In the end, Gladys ends up going living with Billy's aunt, Sis to try and calm herself down.

Billy and Mandy tell Grim it is "Opposite Day" and that, when they say something, they really mean the opposite. Due to his difficulty understanding the concept of Opposite Day, Grim has to do Mandy's chores. Finally, Grim thinks he understands when Billy and Mandy say they "want" pie, meaning they "do not want" pie. However, Mandy then says that when she said it was Opposite Day, it really was not.

Billy and Mandy tell Grim it is "Opposite Day" and that, when they say something, they really mean the opposite. Due to his difficulty understanding the concept of Opposite Day, Grim has to do Mandy's chores. Finally, Grim thinks he understands when Billy and Mandy say they "want" pie, meaning they "do not want" pie. However, Mandy then says that when she said it was Opposite Day, it really was not.

Grim is bored of being left alone while Billy and Mandy are not with him. Grim decides to fulfill his dream by working as a swimsuit model, but, as he is a corpse, he isn't hired. Subsequently, Billy and Mandy give him a makeover to look more human. In the end, Grim gets the job in a TV ad, but he is only in the commercial for a few seconds and is portrayed as an ugly person.

Grim is bored of being left alone while Billy and Mandy are not with him. Grim decides to fulfill his dream by working as a swimsuit model, but, as he is a corpse, he is not hired. Subsequently, Billy and Mandy give him a makeover to look more human. In the end, Grim gets the job in a TV ad, but he is only in the commercial for a few seconds and is portrayed as an ugly person.

Grim misses his life as the reaper of souls and, due to his bet, he cannot return to the Underworld, much to the hilarity of his Underworld co-workers. Having a sudden epiphany, Grim decides to be good and help people rather than try to take their souls. However, Grim's attempts at being good are faced with resistance from people, who are scared off by his appearance.

After watching a movie, Grim teaches Billy to possess people by jumping into their heads. Billy possesses Mandy and makes her do assorted things like flirting with Irwin, kissing Mandy's mother, going into both men's and women's restrooms and eating earthworms. In the end, Billy leaves Mandy's head, but later that night, Mandy possesses Billy's cat, Milkshakes, to maul him as a form of revenge.

After watching a movie, Grim teaches Billy to possess people by jumping into their heads. Billy possesses Mandy and makes her do assorted things like flirting with Irwin, kissing Mandy's mother, going into both men's and women's restrooms and eating earthworms. In the end, Billy leaves Mandy's head, but later that night, Mandy possesses Billy's cat, Milkshakes, to maul him as a form of revenge.

Billy, Mandy, Grim and Pud'n are part of the "Person Scouts" (a Boy Scouts-esque organization) and need to sell cookies in order to win a badge. However, as Billy eats all of the cookies, Grim proposes to bake their own cookies using his aunt Kali's secret recipe. The cookies are a success and the troupe wins the contest. In the end, at the Person Scouts awards ceremony, aunt Kali reveals that the secret recipe contains insects, but everyone continues eating the cookies anyway.

While Spring cleaning in the middle of November, Billy takes an old, cursed lamp from Grim's trunk. When he gives it a rub, he releases the curse Grim had warned them about: his own mother. Having three wishes to make, Billy wastes his wish by wishing to know what to wish for. Mandy wishes Billy and Grim would "shut up", so Grim never gets to make his wish. Then, Mandy decides to make the last wish to whoever makes her the happiest. In the end, Mandy wishes everyone in the world would go away, which she is glad about.

After having a nervous breakdown and leaving the house in the first episode, Billy's mother, Gladys, returns. She meets Grim again and, this time, she plans to destroy him once and for all. When Grim goes to the kitchen for a glass of water, Gladys attacks him and shatters his skeleton. In the end, Grim assures the kids that Gladys has won the battle but not the war.

With Irwin not answering the phone, Billy's parents missing and Mandy saying she wants "Billy for dinner", Billy and Grim assume Mandy is a cannibal who ate Billy's parents and friends. Looking for proof, Billy and Grim find tiki figures and arrangements for a celebration in Mandy's backyard. Ultimately, it is revealed that they are just celebrating Billy's birthday. Still, Mandy burps out Irwin's glasses.

Billy, Mandy, Grim and Pud'n are part of the "Person Scouts" (a Boy Scouts-esque organization) and need to sell cookies in order to win a badge. However, as Billy eats all of the cookies, Grim proposes to bake their own cookies using his aunt Kali's secret recipe. The cookies are a success and the troupe wins the contest. In the end, at the Person Scouts awards' ceremony, aunt Kali reveals that the secret recipe contains insects, but everyone continues eating the cookies anyway.

It's Halloween, Billy, Mandy and Grim go trick-or-treating. Grim mistakes a woman for Atrocia, the host of the all-night Halloween marathon on TV and goes to talk to her. Upon looking at her face, Grim realizes his mistake; however, the woman mistakes Grim for her son, Gregory, and takes him home. At the same time, Billy mistakes Gregory for Grim and he and Mandy take him with them. In the end, Billy and Mandy take Gregory back to his mother and Grim goes back with them.

Nergal, the fiend from the center of the Earth, returns to the surface, emerging a carnival with him, trying once more to make friends. In the following, Billy tries to help Nergal make friends by being considerate, but Nergal fails to apply correctly his advice. When Nergal is told that Grim was forced to be Billy and Mandy's friend-slave, Nergal then decides to force the world to be his friends by turning them into dark beings similar to him. In the end, Nergal turns Billy, Mandy, Grim and even the viewer (thus breaking the fourth wall) into one before the episode ends.

Billy tells Grim to help him throw a surprise birthday party for Mandy. Then, a reluctant Grim helps Billy prepare a cake while keeping it a secret from Mandy. In the end, a somewhat surprised Mandy reveals that her birthday isn't for the next five months, something that Billy already knew about.

Billy and Irwin have been playing their favorite video game, Beasts and Barbarians, for three days non-stop. In an attempt to stop their video game addiction, Grim transports them all to a real-life version of the game. Seeing as Billy and Irwin are still doing good in their quest, Grim increases the difficulty by manipulating the traps himself. In the end, Billy, Mandy, and Grim return home escaping from a giant cyclops, while Irwin remains trapped.

While going to the shopping mall with Billy and Mandy, Grim spots the beautiful Eris, the goddess of discord and chaos, and tries to ask her out. However, Eris is not interested in the skinless Grim, but in the muscular Adonis. Then, Eris invites Mandy to join her in creating chaos using the Apple of Discord. Although initially they get along, Eris pulls a prank on Mandy, who subsequently tries to get revenge. In the end, Mandy fools Eris into thinking that Adonis is in the movie theater, and Eris accidentally kisses Grim.

Billy, Mandy, and Grim go to the museum on a school trip. There, they meet Hoss Delgado, self-appointed hunter of the paranormal, who upon spotting Grim, tries to eliminate him. Subsequently, Grim and Delgado engage in a fight. Finally, Delgado quits hunting Grim when he realizes Billy and Mandy control him. In the end, Delgado continues his adventures and is seen fighting a werewolf.

Billy eats too much junk food that makes him feel sick. Grim prepares him a remedy using his granny's recipe, but this medicine makes a parasite to start growing in Billy's back, which Billy names Yap-yap. In the following, Billy and Yap-yap continue eating junk food, so Mandy suggest to use the antidote to the original remedy. Eventually, Yap-yap, now looking like a smaller version of Billy, detaches himself from Billy (which would have technically cured Billy without the need of him drinking the anitdote), and tries to escape from the antidote. In the end, Yap-yap drinks the antidote and is destroyed.

Billy is constantly provoked by a bully named Sperg and runs over to Grim for help.

After taking the Underworld's "Bad Book" from Grim, Billy becomes possessed by an evil entity. Then, Billy steals Grim's scythe, and uses it to open a portal to summon Yog-Sothoth. In consequence, Mandy calls for Hoss Delgado to battle Billy. It is revealed that the portal can only be sealed by throwing the book into it. As Billy eats the book, Mandy throws Billy himself into the portal, restoring everything to normal. Instants later, a portal opens up and Billy comes out saying that they didn't want him there.

Mandy and her parents leave the city for a day, which makes Billy feel lonely. Then, Grim uses his supernatural powers to create a fake Mandy with pieces of dolls and toys for Billy to play with. However, the "new" Mandy is too aggressive with Billy, and he starts fearing her. The next day, the real Mandy returns home, and promptly destroys the new Mandy while in the see-saw.

In this musical episode, which pays homage to Little Shop of Horrors, Billy befriends a brain-eating meteor that falls from the sky. With Billy's help, the creature grows bigger and eventually eats the brains of all people in Endsville (turning them into zombies with glowing green eyes). The last brain he eats is Mandy's, which results in the creature transforming into a brain-eating Mandy. The song featured is BRAINS!, composed by goth artist Voltaire specifically for this episode.

Billy, Mandy, and Grim eat moldy pizza leftovers, and after falling asleep, they have nightmares. Billy dreams of cute bunnies which turn into monsters; Grim dreams of an endless number of bossy Mandys; Mandy dreams of being pulled into a volcano and then commanding demons at the rhythm of music, in a scene that reminisces the Night on Bald Mountain segment of Fantasia. In the end, Mandy reveals that her dream was actually very pleasant, and she eats the last slice of the rotten pizza.

Billy hatches a giant spider.

A headless man from Grim's past uses Billy to steal Grim's scythe.

At a father-and-son picnic, Billy re-encounters with his spider "son", Jeff, in a dirty bathroom. Once again, Jeff tries to make Billy love him as a true father does, but Billy remains terrified of all bugs. Mandy tells Jeff he is being too nice, and to get Billy's attention he needs to be meaner. After being coached by Mandy, Jeff finally snaps and ensnares Billy in his spider web, forcing Billy to say he loves him.

After spilling salt in a restaurant, and not throwing salt over his left shoulder, Billy starts having an unusual amount of extremely bad luck. The next day, Grim analyzes Billy and finds out he has a "Catastrophe Snail" attached to his brain, which is causing him the bad luck.

General Skarr buys a home in Endsville and becomes Billy's neighbor. After Skarr invites Billy into his new house, Billy mentions Grim's scythe as ,he strongest and most powerful weapon in the entire universe, and Skarr tries to battle his desire to be evil again. Eventually Skarr steals the scythe but Mandy proves to be even scarier than he is, and takes it back.

Lord Pain, a fearsome warrior from the Plain of Eternal Suffering, appears in Billy's house looking to serve his master, Grim. Lord Pain is put to clean the bathroom, and is confused as to why Billy and Mandy treat Grim the way they do. Eventually, Lord Pain realizes that Mandy is to be his real master, and prepares mashed potatoes for her.

In this short, set in the Stone Age, a child version of Grim undertakes his first assignments as the Grim Reaper. When he goes to visit a cave witch, she shows him his terrible future being abused by Billy and Mandy

When Billy, Mandy and Grim go playing golf, they encounter boy wizard Nigel Planter again, who is there hiding from the dark wizard Lord Moldybutt. They head back to the School of Sorcery, where they keep on running into Moldybutt, who warns them to stay away from the "Chamber Pot of Secrets" hidden in Dean Toadblatt's office. It is revealed that Lord Moldybutt is actually Toadblatt, who was disguising himself to scare off Planter. Note: The title is a spoof of Harry Potter and the Chamber of Secrets.

Billy's first cousin from the center of the Earth, Nergal Jr. goes to school for the first time, but he is worried that people may not like him. Soon enough, Junior becomes bullied by Sperg, with Miss Butterbean's allowance. Billy suggests Junior to use his shapeshifting abilities to take on the form of Miss Butterbean, so Junior can help him pass a math test. Junior likes the idea, but he morphs into Miss Butterbean to get revenge on Sperg instead. Sperg is seen living in the center of the Earth as Junior's pet.

Trying to get revenge at Mandy for bossing them all the time, Billy and Grim put her in the "Mask of the Beast". Mandy must be nice and friendly while wearing the mask, or else she will become a hideous monster. Failing to remove the mask herself, and struggling to be kind to Billy and Grim, Mandy gradually turns into the beast. Billy and Grim ask Mandy to smile while she gives them a sponge bath, but this turns out to be too hard for Mandy. She fully transforms into the beast and punishes them instead.

During a thunderstorm, a lightning bolt hits Grim's scythe, transporting Billy to Asgard, land of the Norse gods. Mandy and Grim go searching for him, while a Viking wearing Billy's shirt remains at his house as a substitute. In Asgard, Billy learns about the endless battle in Valhalla, in which if a warrior dies, he is resurrected to continue fighting. Billy is surprisingly good at killing other Vikings, so Mandy and Grim are unable to convince him to return home.

When Billy and Mandy have a brief fight, Billy says he never wants to speak to Mandy again. The next day, Billy is over his grudge, but Mandy has already decided to find a replacement for him. Mandy introduces Bobby, the new "Billy", who turns out to be a better friend than Billy, even gaining the affection of his parents, but who also wants to take over Billy's life. A jealous Billy uses Grim's scythe to open a portal and send Bobby to another dimension.

When Billy hangs out at Irwin's house, he finds a living mummy in the bathroom. Seeing as Irwin gets nervous, and as Billy has never met Irwin's mother, he suspects she is the mummy. To scare him off, Irwin's dad tells Billy he has the "curse of the mummy". Billy is attacked by insects and snakes while he tries to find out the truth about the mummy. It is later confirmed that Irwin's mother is in fact the mummy, but no further explanation is given as to how Irwin's family works or how he was conceived.

At school, Billy, Mandy, and Irwin look for a club to join. Irwin plans to join the Macrame club to meet girls; Billy inquires on the Junior CIA club, which forcefully recruits him; Mandy joins the "Secret Snake Club", a snake-themed club consisting of three geeks. The nerds reveal that their "secret agenda" is to resurrect Shnissugah, a giant snake which lived hundreds of years ago in Canada, to take revenge against the popular kids, but they lack the power of the Underworld to do so. Mandy calls for Grim, who proceeds to revive Shnissugah through the internet. Billy, as a junior agent of the CIA, stops a criminal plan by Irwin, who was using the Macrame club for personal gain; and Shnissugah turns out to be a tiny, 8-cm (3.14-in) long, harmless snake.

After Grim's robe comes out of the washing machine, Billy and Mandy find Thromnambular, a talking skull with ruby eyes and a number nine imprinted on his forehead. Grim tells them that the skull is a magical artifact imprisoned on Earth that must grant his nine wishes to be free. When Mandy asks Grim why he has not used any of the wishes, Grim tells her that the skull will corrupt the wishes and end up affecting the wisher.

When Billy gets under his house's foundation, he encounters again his "son", Jeff the Spider, who has just laid eggs. Jeff tries to make things right with Billy so he can take care of the baby spiders, as he is going to die after the eggs hatch. Naturally terrified of seeing Jeff, Billy runs away and a wild car chase ensues. The eggs hatch, and Grim decides to refill Jeff's hourglass that represents his lifetime so he does not die and can continue to scare Billy.

After Grim has a nice dream, a nightmare escapes the back of his head in the shape of a supernatural, invisible duck that makes farting noises. The duck follows Grim everywhere, causing him embarrassment with the non-existent farts, and to end up in jail. The duck repeats the strategy, following other citizens, including Irwin and Billy's dad, resulting in all of them going to jail too. The duck tries to annoy Mandy, but she remains imperturbable by its presence. The duck disappears and Principal Goodvibes is really angry, and he gives Mandy 75 days of detention.

Billy and Mandy find a supernatural zipper from Grim's robe, and while Billy uses it to create mischief, Mandy gets herself in a sticky situation.

At school it is time for the "Presidents Fitness Test", but Billy is absolutely unfit for exercise. On the other hand, Nergal Junior uses his shape-shifting powers to become fit at will and excel in every test. Billy asks Junior to transform into a pair of pants that he can wear, so he can run fast and win the 50-meter race. Since Junior has never attempted to transform into inanimate objects he cannot stop running and cannot revert to his human form. Billy keeps running forever while he becomes a national sensation known as the "Fitness Lad". It is revealed that the story was just all a fabrication created by the narrator, who parodies The Twilight Zone.

After Grim's scythe fails to open a portal, he decides to sharpen it, but the blade breaks. Billy, Mandy and Grim go to the Underworld to meet F (a parody of James Bond's "Q"), who is in charge of the Underworld secret gadgets. F unveils Scythe 2.0, which is a new-and-improved sentient, autonomous, thinking and feeling computerized scythe, that Grim uses while his classic scythe is being repaired. When Mandy tells Grim to do his usual humiliating chores, Grim delegates the work to Scythe 2.0, which rebels and decides to reap by itself, starting with Billy and Mandy. Grim saves the kids, takes Scythe 2.0 back to the Underworld, and returns with his old scythe.

When Billy's parents are attacked by an anaconda, Billy suggest visiting boy wizard Nigel Planter, because he can talk to snakes. Planter in fact does not speak to snakes, but to snacks, and instead he asks for Billy, Mandy and Grim's help to win the affections of Huffefnie Pfefferpfeffer, a beautiful witch in the School of Sorcery (and having a striking resemblance to Gladys). Planter tries using a romantic love potion and enchanted chocolates, but they do not work. The guys end up completely forgetting about Billy's parents.

When Billy's parents leave for their second honeymoon, Billy is left alone at the worst possible moment, since he has invited Principal Goodvibes over to dinner so he can recommend him into Rollington Academy for the Gifted. Billy's dad suggest Billy to use Eris, the goddess of chaos, and Hoss Delgado, spectral exterminator, as his substitute parents during the dinner. The dinner is a disaster with Delgado terrorizing Goodvibes, and Eris unleashing giant alien zombie lobsters. Goodvibes forcefully recommends Billy into Rollington Academy, which, as it turns out, is actually a military school.

When Billy, Mandy and Grim notice things have been disappearing in the house, they set out to investigate using a supernatural detector. They find the culprit is a talking "taking tree" in Billy's yard, who has been stealing objects since Billy's dad was a child. To make the tree happy, Mandy and Grim set out to trade the stolen belongings for a highly-valued Mickey Munchle baseball card, which is worth eleventy million dollars. Mandy and Grim return from the baseball shop with the real Mickey Munchle. The tree returns all of the stolen things, but keeps the player.

When Nergal goes to visit Billy's family (his in-laws) for the weekend, he ends up staying with them over a year. When Billy finally asks his uncle to leave, Nergal says he cannot return home because he is a complete failure, having lost at a board game 599 times in a row against his own family, and experiencing constant disappointment elsewhere. Billy and Grim tell him to not worry about being a failure, but to embrace it. After training with Billy and Grim, Nergal returns home and he finally wins at the board game, but he also makes a crack in the ceiling and his home starts filling with lava.

As Billy desires to be "cool" like Sperg, he has an ectoplasmic manifestation coming out of his mouth. The ectoplasm grows full size and turns out to be the ghost of nineteenth-century British poet Lord Byron, who tries to teach Billy to be cool, using elaborate poetry instead of bare muscles. Billy uses a poem to insult Sperg's mother, and Sperg challenges Billy to a duel. Billy and Lord Byron fight Sperg and his gang, but are badly beaten. Byron tells Billy he has been trained in the arts of coolness, and disappears.

As Grim watches the entire season of "My Troubled Pony" (parodying My Little Pony), he learns from Mandy that the show was cancelled and does not have an ending. Grim decides to reap the "Schlubs" (a parody of The Smurfs), 100 creatures that live in Billy's yard, to melt them into gold so he can finance the creation of the series finale. Grim must get past Billy and the aggressive Schlubs themselves, including the single, large female (a parody of Smurfette). After Grim thinks he got the creatures with his scythe, Mandy appears to have used all the gold herself to become rich.

When Billy and Irwin start making prank calls, everybody knows that Billy is behind the calls because every telephone has a caller ID. While Billy searches in Grim's trunk in the basement for something to defeat the caller ID, he finds a skull-shaped phone with no caller ID. Grim warns him to not use the phone, because it is used to call the ancient demon Cthulhu, whose sole appearance makes people go mad, and if awakened will cause the destruction of the world. Despite Grim's warning, Billy and Irwin use the phone anyway, and they are sucked into it by tentacles.

When Billy digs his front yard he finds a frozen caveman, who is actually Fred Flintstone (from The Flintstones), but whom Billy names Jake Steele. Billy tries to acclimate Fred to the modern life but the job is not easy. When Fred is taken to school, he predictably goes out of control, kidnapping Miss Butterbean and running away in Principal Goodvibes' car. The ensuing chase results in Fred crashing into an ice cream truck, becoming frozen again. Instead of reaping him, Billy decides to bury Fred in the yard again. A future is shown where both Billy and Fred are defrosted by brain-eating creatures.

When Billy gets his kite stuck in a tree, he starts throwing objects at it to knock it down, including Mandy and a group of three boy scouts, but all objects get stuck too. Frustrated, Billy and Grim call a druid for help, who in turn trains them to become druids, so the three of them can perform a ritual. Meanwhile, inside the tree, Mandy battles a group of squirrels, and leads the scouts back to the ground. Since the druidic chants did not work against the tree, the druid goes ahead and uses a chainsaw to bring the tree down, but this gets him arrested.

When Billy destroys Grim's favorite childhood toy, Fancy Jake, Grim feels devastated and wishes he had never lost the limbo game that made him become Billy and Mandy's best friend forever and ever. A lawyer appears saying that although the game is legally binding while all parties remain on Earth, it is not if Grim leaves Earth. In consequence, Grim follows the lawyer's advice, opens a mystical portal, and leaves. With Grim traveling aboard his spaceship, the lawyer takes off his disguise and introduces himself as Morg, the Martian Grim Reaper, who is also Emperor of Mars and commands an army of Martian, brain-eating zombies.

As Billy sees Hoss Delgado's manliness is action again, Billy wishes to grow up to be a hero like him. Grim tells Billy that in older times an evident way to become a hero was to slay a dragon. They travel to the Middle Ages so Billy can train under the supervision of the best dragon slayer, Sir Boss Del Guapo, who resembles the present time Delgado. Billy becomes friends with the dragon he was supposed to kill and spares his life, becoming the dragon's hero. Del Guapo finds himself transported to the present, where he has a brief encounter with Delgado.

When Billy finds his "son" Jeff the Spider lying in his bed with "Spider Pox", he goes to Mandy for help to get rid of the giant spider. While ignoring Billy, the next morning Mandy awakens afflicted by Spider Pox too, developing four additional arms and the ability to produce spider web. Mandy's condition progresses and she completely turns into a giant spider, who captures Billy's parents and Grim. Grim tells Billy that, to cure Mandy, he must use the venom of the spider that infected her. While Billy successfully gives Mandy Jeff's venom, he also carried the virus and infected the people of the city, who have all turned into spiders.

As Billy notices Mandy and Grim's usual negative attitude, he wishes they were in a magical land of happiness, so Grim transports them to an enchanted forest. Billy enjoys the relaxed surroundings until he meets a cantankerous and sour unicorn named Mary-Frances. Billy tries to change Mary-Frances attitude, but she is reluctant due to an earlier trauma of not being able to swim and follow the other unicorns into the sea. After Billy teaches Mary-Frances to swim, she feels happy and finally can join the other unicorns, but they turn out to be bullies, the real reason she never joined them in the first place. Billy stays with the unicorns and Mary-Frances goes back with Mandy and Grim to watch TV.

As Billy, Mandy, Grim, and Irwin hang from a rope about to be eaten by a giant sea serpent, Irwin wonders how they came into that trouble. Billy and Grim each tell separate stories on how they originally became best friends forever and ever. Billy's fantastic story is about him and Mandy being space patrol officers who collect the Grim Reaper's bones, cloak, and skull to summon him; Grim tells a story on how the evil Mandy and his pet servant Billy managed to capture him inside a containment unit (parodying the Ghostbusters' ghost traps). Mandy quickly tells the real story, and footage from the first episode is seen, before the four are swallowed whole by the serpent.

As General Skarr is once again annoyed by Billy, Hector Con Carne and Major Dr. Ghastly arrive in his house with the intention of luring him back to the recently relaunched Evil Con Carne world domination organization. Although initially refusing to rejoin, Skarr later accepts with the condition that Billy and the other neighbors be destroyed. After a few weeks of living together and preparations, Evil Con Carne's ultimate weapon is revealed to be an army of tanks that shoot giant rubber bands. Skarr's all-out attack over the neighborhood is foiled when Billy tricks Hector into shooting Skarr's garden and they get into a fight.

When Mandy finds Billy playing with Grim's gigantic dog, Cerberus, she tells Grim to keep Billy under tight control because she needs a good night of sleep to be ready for the next day's test. With a little persuasion from his own dad, Billy tries to wake up Mandy at night, so she will fail the test and he can score higher than her for the first time. After Grim spends the night guarding Mandy's house from Billy, the latter succeeds in waking up Mandy. It is revealed that this Mandy is in fact Irwin, used as a decoy by the real Mandy, who slept in her dog's house. Mandy passes the test, and Grim is punished for not guarding her properly.

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.

When Billy is sent to bed after playing with his Dr. Brainiac action figure, he wishes he had an adventure. He notices a strange light outside and wanders into a corn field to investigate; he encounters Sperg, and both of them got caught by a UFO's tractor beam. Inside the extraterrestrials decide to experiment on them.

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.

As Billy, Mandy, and Irwin need to write a school report on tall tales, Grim tells outrageous tall tales about Pecos Billy (based on Pecos Bill), Paula Bunyan (based on Paul Bunyan), and John Henry. In Grim's stories, Pecos Billy (Billy) tames a twister using his personal laser-shooting cow-like spacecraft, saving an Arizona trailer park; Paula Bunyan (Mandy) uses her blue ox companion, Babe, to stomp over a villain, creating the Grand Canyon in the process; John Henry (Irwin) digs through a tunnel so fast that he breaks the laws of physics and bursts into the "eighth dimension". After Grim tells them the stories, Mandy informs Billy and Irwin that he is trying to get them F's.

When Billy's dad drives Billy, Mandy and Grim to the hamburger restaurant, they somehow end up in Mexico. There, the people are celebrating Dia de los Muertos, but local kids say it may be the last celebration ever, because Del Uglio, a masked and ugly luchador, is set on stealing the "Golden Nose of Chipotle", a prehispanic relic on which the festivity is based. To get to the nose, Del Uglio has one half of the map, while the other half is held by his lost twin brother, who turns out to be Billy. Grim defeats Del Uglio, but it is Mandy who keeps the golden nose for herself, which makes her rich.

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