As Billy behaves more reckless than ever and can't stop breaking everything in sight, Mandy thinks he should go some place where he can release all his urge to destroy until he gets tired of it. Then, Mandy, Grim and Irwin go to Level 9, home of the fearsome warrior Lord Pain, to convince him to take Billy. Meanwhile, Billy receives psychological treatment and it is revealed that his desire to destroy stems from lack of attention when he was younger. Then, Lord Pain abducts him, and together they start destroying everything in Level 9, which apparently is uninhabited. In the end, Billy is still not satisfied, so he and Lord Pain return to Endsville and carry on breaking everything.

When Grim leaves the house to meet someone he met on the internet, Billy looks inside Grim's trunk for something to entertain himself. Then, Billy finds a magical talking Rubik's Cube, which releases the demon Pinface, who has bowling pins in his head (a parody of Pinhead from Hellraiser). Then, Pinface proceeds to call his minions to conquer Earth, but the minions are more interested in throwing a house party. Later, it is revealed that Grim and Pinface already know each other, and Grim even broke up with Pinface's sister. In the end, Billy's father cheats and solves the magical cube by rearranging the stickers, trapping Pinface and his minions inside it again.

As Billy realizes the three geeks of the Secret Snake Club get doctor's notes to avoid Physical Education (P.E.) class, he wants to know their secret to avoid the class too. Then, all the boys in the class join the club and all, except Billy, get doctor's notes from Billy's dad, who poses as a doctor. Then, while Billy is the only one exercising in the class, the Snake Club summons a snake to destroy the gym. However, since the invoked snake is tiny, Sperg uses Grim's scythe to make it a giant. In the end, Mandy and the other girls beat the boys and their snake because they did appreciate the P.E. class as an outlet for their aggression.

When Billy, Mandy and Grim attend an Ancient Egypt exhibit at the museum, they meet with Irwin who explains that, as his mother is a mummy, they are visiting Irwin's grandfather, the great Pharaoh King Popen Locken. Later that night, Irwin's grandfather visits Irwin in his room and offers him the Pharaoh's crown and the possibility of building his own pyramid to attract women; Irwin accepts, calling himself King Tooten Pooten, and soon they turn the citizens into slaves to build the pyramid. In the end, against his mother's wishes, Irwin decides to finish the pyramid; however, there is something he didn't anticipate, as he, the Pharaoh, needs to remain entombed inside it.

When Billy fails an important test, the result of which will go into his permanent record, he asks Grim to magically alter his grade from an "F" to an "A"; as Grim reluctantly changes the grade, Billy becomes a genius, but reality is thrown completely off balance. Then, Mandy and Grim go back in time to stop the past Grim from helping Billy, but it doesn't work. They keep going back in time to different epochs, each time meeting another Grim, eventually trying to stop Billy's ancestors from conceiving him, but nothing works. After meeting Billy's distant dinosaur relative, the episode ends abruptly as Grim wonders what the end of this could be.

After watching the Unsolvable Mysteries TV show, Grim realizes he forgot a million years ago to reap the Abominable Snowman living in the Himalayas. Then, Billy, Mandy and Grim go there to finish the job and also to obtain videographic proof of the snowman's existence. The Yeti, who likes to be called Abom, manages to escape Grim several times, before finally being trapped by the moving glacier. In the end, as Grim watches the TV show again, it is apparent that he may have forgotten to reap the Loch Ness monster too.

When Nergal comes to tell the guys about his new pizza joint, Grim thinks he can do better by using his Granny's recipe. Then, a pizza war ensues between Nergal's Pizza and Grim's Pizza, with each pizzeria launching TV ads and discrediting each other. Finally, Nergal Jr. uses his shape-shifting abilities to infiltrate Grim's pizza and replace Granny Grim's hot sauce with a "ghastly elixir". The result is pizzas becoming monsters and attacking the city, and the citizens developing parasites similar to Nergal. In the end, Nergal and his family leave the city just as Grim's sauce explodes.

After Billy, Mandy and Grim are disappointed with the SassyCat amusement park submarine attraction, Grim uses his powers to take them to the bottom of the ocean to have a real magical adventure. There, they are sentenced to death for trespassing into the Googen Kingdom by King Triceps, a wrestling merman. However, the king's daughter, Hariel, also a mermaid, stops the sacrifice and tries to marry Billy in order to inherit the kingdom. Then, it is revealed that King Triceps is actually Hariel's sister, the sea witch Uvula, who also tries inherit the kingdom. A cat fight ensues between the two ladies, which ends when Billy agrees to marry both of them. Then, the plot is eventually revealed to be a story Billy is telling to Miss Butterbean, who initially asked him what happened to his report.

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. In the end, 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. Special Guest Stars: Phil LaMarr as Hector Con Carne, Frank Welker as Boskov, Grey DeLisle as Major Dr. Gastly Note: This is a crossover episode with the series Evil Con Carne

As General Skarr has trouble finding a job, the recruiter tells him to attend anger management classes if he wants to work again. Then, Skarr finds out Mandy and Grim are attending too, Mandy for staring at the school monitor, and Grim for enjoying too much his job. The instructor of the class, Larry, turns out to be a peace-loving, short man riding a tricycle, who teaches the trio ways to calm down when angered, including counting to ten, and using harmless weapons to let go of their anger. In the end, Larry invites Billy to the class, and Mandy, Grim, and Skarr all manage to contain themselves; however, Larry himself suffers an episode of rage over a parking space and he is arrested.

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. Then, 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 apparently succeeds in waking up Mandy. However, 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. In the end, Mandy passes the test, and Grim is punished for not guarding her properly.

When Billy, Mandy and Grim once again go to the beach, Grim warns Billy to avoid swimming too far, because the "undertoad", a frog-like creature, will try to drag him into the sea. Naturally, Billy encounters the undertoad, and he barely makes it back to the beach. Then, with the dangers of the sea averted, the guys go back home, but the undertoad is set on bringing Billy down, that he follows him to his house. The next day, the undertoad becomes a constant annoyance to Billy, even at school. In the end, Grim and Mandy capture the undertoad, and set sail to release him at sea, where they meat the giant Mama undertoad.

When Irwin lacks the courage to ask Mandy to go with him to the Valentine's Day school dance, he tells Nergal Jr. to do it for him. Then, Mandy mistakes Junior's invitation for his own, and surprisingly accepts to go with him, which naturally makes Irwin jealous. Then, with the ill advice received from his father, to be possessive with Mandy, at the dance Junior becomes overprotective of her, that eventually he and Irwin start fighting, throwing punch at each other and ruining the ball. In the end, it is revealed that this was Mandy's true intention all along so that no one could enjoy Valentine's Day.

When Billy accidentally food-poisons Miss Butterbean, Principal Goodvibes offers Grim the job of substitute teacher, which Grim accepts as now Billy and Mandy have to obey him. In the following, Grim sends misbehaving students to the "Detention Dimension", a place of eternal classroom punishment, until only Mandy remains in his class. Then, Grim tricks Mandy into opening a portal and she is dragged into the dimension too. In the end, Mandy proves to be more terrifying than Miss Slither, the giant, rattlesnake-like creature in charge of the Detention Dimension, that Mandy escapes the place and takes revenge on Grim by sending him there too.

When Billy is sent to bed after playing with his Dr. Brainiac action figure, he wishes he had an adventure. Then, he notices a strange light outside and wanders into a corn field to investigate; there, he encounters Sperg, and they are both abducted by aliens who experiment with them. Later, when they return home, it is revealed that Sperg has a bomb implanted in his head, and also that there is a shortage of dairy products; Billy explains that the aliens are stealing Earth's dairy products because they are werewolf-like creatures who need cheese, and they have already mined all the cheese in the Moon. In the following, Billy's crazy story is confirmed when too many UFOs appear. Then, Billy says they must assemble a team of diary superheroes, the Green Squeaker (Billy), Milk Mandy, the Cheese Reaper, and Diary Boy (Sperg), to combat the aliens, but everybody is opposed to the idea. Later, the four of them have been captured and are sent to the Moon to be destroyed, but they escape and

When vampire hunter Lionel Van Helsing prepares to kill Dracula, Billy, Mandy and Grim arrive to stop him, since, after all, Dracula is just senile and harmless. Then, Van Helsing reveals the source of his hatred: in the past, he and Dracula were "best friends forever", until Dracula used his irresistible dance moves to marry Tanya, the woman of his dreams. Later, Tanya arrives too, revealing that she is none other than Irwin's grandmother, making Irwin half-vampire on his father's side, and half-mummy on his mother's side. In the end, Van Helsing leaves, but Dracula is unsatisfied with his newfound family of nerds.

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 "8th dimension". After Grim tells them the stories, Mandy informs Billy and Irwin that he is trying to get them F's.

When Billy, Mandy and Grim go to a joke shop, they find the owner is former boy wizard Nigel Planter (a parody of Harry Potter), who reveals that his powers diminished and was kicked out of Toadblatt's School of Sorcery. Then, Planter steals Grim's scythe and heads to the school to exact revenge on those who wronged him. In the following, the guys seek the help of Planter's sworn enemy, Lord Moldybutt (a parody of Lord Voldemort), to find the school. In the end, Grim recovers his scythe, and Moldybutt turns out to be in fact only a real estate agent, who informs Planter that he is the heir to the "Peanuts by Planter" farming company.

When Grim can't take any more abuse from Mandy, Billy tries using Grim's scythe to shrink her to mouse size. However, instead of shrinking, Mandy becomes a giant and destroys Billy's house. Although Mandy enjoys being a giant for a while, there are inconveniences, as she keeps growing as time passes, and she wants to return to her normal size. However, Billy is the only one who can cancel the curse he put on Mandy, and he refuses to do so. In the end, Mandy grows bigger than the planet, and she finds herself in the "Realm of the Infinite" with other creatures that, like her, grow at infinite pace. Naturally, Mandy starts bossing them around to please her.

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. In the end, Grim defeats Del Uglio, but it is Mandy who keeps the golden nose for herself, which makes her rich.

When Billy starts taking pictures with a camera found in Grim's trunk, Grim tells him that is an Underworld's True-heart Camera, which shows the real essence of a person's heart. Then, when Mandy takes Irwin's picture, it is revealed that he is actually half-good and half-evil. Irwin explains that although he was born evil, his dad taught him about love and respect, and he had a change of heart. Upon knowing this, and against her own wishes, Mandy also experiences a painful change, turning good. Finally, Mandy and Irwin kiss. However, this kiss makes Mandy revert to her old dark self, which was Irwin's true intention, as he likes her just the way she is.