The Grim Adventures of Billy & Mandy (season 1)

Toadblatt's School of Sorcery: In a parody of the Harry Potter series, Grim sends Billy and Mandy to a sorcery school so the latter duo could avoid boring summer camps they were supposed to go to. The sorcery school is owned by Dean Toadblatt, an anthropomorphic frog. Billy and Mandy are sent to the most hated house on the school, Weaselthorpe, while Grim becomes a prefect for a more loved house, Gunderstank. Billy and Mandy team up with boy wizard Nigel Planter to sabotage Gunderstank. Planter takes all the credit for the sabotage (which was Mandy's idea), but he is punished once he is found out by Toadblatt.

Educating Grim: Billy and Mandy take a reluctant Grim to school with them. Mandy's nemesis, Mindy, befriends Grim to annoy Mandy and Billy calls for their other friend, who is Abraham Lincoln. Mandy devises a plan in which Mindy ditches Grim, and keeps Abraham as her friend instead.

Night of the Living Grim: Grim is lying sick in bed with "Encroaching Doom Syndrome". The Underworld doctors are not able to help Grim, and he becomes a human being. Back in Endsville, Grim seems attractive to women, but he ends up being punched by jealous boyfriends, especially Billy's dad Harold. Grim covers himself in the mucus that he produced when he was sick and becomes a skeleton again, and Billy tries it too.

Brown Evil: Part 1: Taking inspiration from his Pat the Baker video game, Billy decides to bake chocolate brownies. Billy uses "Evil Powder" from Grim's old trunk instead of salt, and the resultant brownies stink. Mandy tells Grim to get rid of the brownies, and he reluctantly does, but he also stores some of them in his skull. Soon, the stench of the brownies spreads through the world and starts resurrecting dead people, animals, and even food, as zombies.

Mandy, the Merciless: On a hot day when Billy, Mandy, and Irwin are bored, Grim uses a crystal ball to show them the future. In the distant future, Mandy has turned herself into a giant worm-like creature to be immortal, and now rules the whole world. Mandy gives false information to a clone of Billy to capture the members of a resistance that try to defeat her. The episode parodies the science fiction novel God Emperor of Dune by Frank Herbert.

Creating Chaos: When Billy, Mandy, and Grim go fishing, Eris, the goddess of chaos, gets Billy to help her use the Apple of Discord to create chaos (after her father grounded her). Instead of using the apple, Billy becomes distracted with his own idiotic errands, leading Eris to go insane. Billy finally decides to start creating chaos, but Eris is already too altered that she runs away.

Who Killed Who?: After excluding Mandy from their board game Who Killed Who? for being a girl, Billy and Irwin mistakenly throw their dice into the backyard of a haunted house. Grim warns them about the ghost of Mrs. Doolin, a lady that lived there. Mandy dares to go inside to retrieve the dice, and she befriends Mrs. Doolin, who is alive and well, and who says that all the stories told about her (that anything that went beyond her fence into her garden never came back) are inventions from Grim, whom she beat long time ago at a staring contest. Fearing for Mandy's life, Billy also ventures into the house, but Mrs. Doolin and Mandy scare him away by posing as ghosts. It appears that Mrs. Doolin is in fact a ghost, and when she meant "beating Grim", it meant that she "beaten death".

Grim in Love: When Billy, Mandy and Grim go to the beach, Grim falls in love with a goth woman named Malaria. Grim is having a good time with his girlfriend, but Mandy assures him that will change when he tells her that he is not human. In the following date, Grim demonstrates his supernatural powers while dancing and, as predicted, Malaria leaves in panic.

Crushed: At school, Mandy rejects Irwin's invitation to go to the school dance with him. Billy introduces his foreign and mysterious, new friend, "Piff", and Mandy becomes desperate when she realizes that she has developed a crush on him. Mandy asks Grim to cut her heart out to stop being in love, but Grim has a better idea and gives Mandy a makeover, turning her into a really seductive figure. Piff gets a crush on Mandy (the same way Irwin had gotten before), who takes the opportunity to brutally turn him down.

The Crawling Niceness: Billy takes a big egg found in Grim's trunk and hatches it expecting a duck. Instead, Jeff the Spider is born, who considers Billy his father. Despite Jeff trying to please Billy in any possible way, Billy is terrified of Jeff and wants him squished. The exterminator chose not to squish Jeff because he is a nice bug.

Smarten Up!: Billy is worried about failing an upcoming Math test, so Grim gives him a "bookworm", which will make him much smarter. Milkshakes, Billy's cat, eats the worm instead, and is forced to tutor Billy. Billy is still an idiot in the end.

Son of Nergal: Billy and Mandy are sent to "Winter Camp", where they meet Nergal's son, Nergal Jr. Just like his father, Junior tries making friends, although not in the best way possible. Junior attacks the campers, freezes them and, using his shape-shifting abilities, takes over their appearances. Billy decides to be Junior's friend, but he is scared away at the moment Junior shows him his true form.

Sister Grim: After being accidentally hit by Billy, Grim lands in a can of white paint in a remote convent. Due to his appearance, still with the can in his head, Grim is mistaken for "Sister Big Mamma" by little cherubic nuns. Grim has a great time with the friendly nuns, until Billy and Mandy come looking for him. When the nuns realize the truth about Grim they get angry at him, but also help him go back home by sending him flying away with another punch.

Terror of the Black Knight: After being impressed by Irwin's realistic armor at the medieval fair, Billy wishes for a fancy armor too. Grim gives him the "Cursed Suit of the Black Knight". When Billy needs to go to the bathroom, the curse is revealed to be that the armor cannot be taken off until the person wearing it beats someone in a competition. Billy desperately tries to defeat other people at various contests, he but fails to come out victorious. He defeats Mandy at a breakdance contest in which Mandy decided not to participate, but he does not need to go to the bathroom anymore.

Battle of the Bands: Billy wants to join Sperg's garage band, "Purple Filth", and take part in the upcoming battle of the bands. After witnessing Grim's prowess with the electric guitar, Sperg invites Grim instead. Billy's dad, adopting the rock and roll persona of "Mogar", decides he and Billy should go to the contest to make a surprise appearance. Billy impresses the audience with his armpit sounds.

Grim for a Day: After a lousy night for Grim, Billy and Grim argue about who has the hardest time, the kid or the Reaper of Souls. Mandy proposes they switch places for the day to find out. Grim seems to be having a good time, acting like a silly kid, while Billy is bored waiting for his old victim, Mr. Voorhees, to open the door. Billy transforms into a short skeleton, while Grim transforms into a taller version of Billy.

Billy's Growth Spurt: 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.

Hoss Delgado: Spectral Exterminator: 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 own adventures and is seen fighting a werewolf.

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

To Eris Human: 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.

Meet the Reaper: 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 own command.

Note: Based on the theatrical pilot film, Billy & Mandy, this is the only episode not produced by Cartoon Network Studios, having been produced in 1999 by Warner Bros. Animation's subsidiary Hanna-Barbera.

Skeletons in the Water Closet: 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.

Get Out of My Head!: 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.

Look Alive!: 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.

Something Stupid This Way Comes: 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.

A Grim Surprise: 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 here for the next five months, something that Billy already knew about.

Billy, Mandy and Grim go trick-or-treating for Halloween, and Irwin is left behind because he needs a scarier costume. After pulling a trick on an old lady, and getting some candies, Grim tells the story of why people pull pranks, which he was partially responsible for. He tells about Jack (voiced by Wayne Knight), a prankster of the old Endsville who just never knew when to stop. One day, the citizens decided to punish him for his constant pranks, and they pulled a prank on the queen, but signed it "From: Jack"; in consequence, the angry queen sent a knight to kill Jack. When Grim went for Jack's soul, Jack stole his scythe. In return for his scythe, Grim promised Jack eternal life, but after closing the deal, Grim takes his scythe and cuts Jack's head off, showing that no one will "EVER" see his face again. Afterwards, Jack decided to use a pumpkin for a head, becoming Jack O'Lantern, and, suffering from the loss of his real head and learning his lesson about pulling pranks too far and whom he does them to, every Halloween he goes out to pull pranks on the citizens of Endsville, and waits 364 more days a year until next Halloween in solitary mode in his own house.

Little Rock of Horrors: In this musical episode, which pays homage to Little Shop of Horrors, Billy befriends a singing brain-eating meteor (voiced by Voltaire) that falls from the sky after when everyone doesn't want to play with him because they are busy. 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 pink, brain-eating Mandy meteor.

Fiend is like Friend Without the "R": Billy wanders into a junkyard, where a massive hole in the earth opens up and pulls him down in. Later, Mandy and Grim get pulled in as well. They land at the center of the Earth, which is home of Nergal, a devilish creature. The lonely Nergal, who has been watching Billy and Mandy for some time, wants Grim to hand over the kids to him so they can be his friends forever. Grim happily leaves the kids behind as he returns to the surface; however, he later goes back for them because he can't handle the guilt of abandoning his friends. In the end, Grim is defeated by Nergal's electrified tentacles, but Mandy defeats Nergal merely by kicking him in the shin.

Recipe for Disaster: 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.

Grim or Gregory?: 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 Gregory is now Grim, and does not have a stomach. 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.

Grim vs. Mom: 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.