The Grim Adventures of Billy and Mandy

Billy's pet hamster, Mr. Snuggles, turns 10, which leads the Grim Reaper to come for him. Billy's friend, Mandy, offers to challenge the Grim Reaper to a game of limbo in exchange for Mr. Snuggles' life, setting the condition that if the Grim Reaper loses, he must spare the hamster and become their friend. During the game, Mr. Snuggles unexpectedly attacks the Grim Reaper, as instructed by Mandy, causing him to lose.

Gladys grows increasingly worried after spotting a figure named Grim in Billy's bedroom and bathroom, leading her to believe her son is in danger. Her husband, Harold, dismisses her concerns as baseless. Eventually, overwhelmed by her anxiety, Gladys relocates to live with Billy's aunt, Sis, in an effort to regain her emotional stability.

In the episode, Billy and Mandy deceive Grim into thinking it is "Opposite Day," a day where their words carry the opposite meaning, leading to confusion and causing Grim to perform Mandy's chores. After Grim believes he has grasped the rules, Mandy clarifies that there was never an actual Opposite Day.

Feeling lonely while Billy and Mandy are away, Grim attempts to become a swimsuit model but is rejected because of his undead appearance. With the assistance of his friends, he undergoes a makeover to appear more human and secures a minor role in a television commercial, although he is only shown briefly and in an unflattering manner.

Grim, unable to return to the Underworld due to a bet, struggles with his new life among the living and longs for his former role as a soul reaper. Encouraged by a sudden realization, he attempts to do good, but his efforts are hindered by the fear and discomfort his appearance causes in others.

Grim instructs Billy on how to possess people by entering their minds, and Billy uses this ability to take control of Mandy, causing her to exhibit various unusual behaviors. After Billy leaves Mandy's body, she later seeks revenge by possessing his cat and attacking him.

In *The Center of the Earth*, Billy, Mandy, and Grim fall into a mysterious hole in a junkyard and are transported to the Earth's core, where they meet Nergal, a lonely and sinister creature who wants to befriend them. Nergal attempts to keep the trio with him, but Grim initially abandons them before returning out of guilt. Ultimately, Grim is captured by Nergal, but Mandy defeats him with a simple yet effective kick to the shin.

In one episode, Billy, Mandy, Grim, and Pud'n join the "Person Scouts" and participate in a cookie-selling challenge to earn a badge. When Billy consumes their entire supply, Grim proposes they make their own using a mysterious recipe from his aunt Kali, which helps them succeed in the contest. At the awards ceremony, it is revealed that the cookies contain insects, but the group continues to enjoy them regardless.

During a spring cleaning in November, Billy discovers and rubs a cursed lamp from Grim's trunk, unintentionally freeing his mother, who had been trapped inside. Given three wishes, Billy squanders one by wishing he knew what to wish for, and Mandy uses the last wish to make everyone in the world disappear, a choice she later regrets.

After experiencing a breakdown, Gladys returns home and confronts Grim, determined to defeat him. She attacks him in the kitchen, causing damage to his skeleton, but Grim warns the children that the conflict is far from over.

Billy and Grim become suspicious that Mandy is a cannibal after she says she wants "Billy for dinner" and they discover strange items in her yard. However, they later learn it was actually part of a birthday celebration. Mandy later burps out Irwin's missing glasses.

On Halloween, Billy, Mandy, and Grim go trick-or-treating, but Grim mistakes a woman for the TV personality Atrocia and is mistaken by her for her son, Gregory, who has no stomach. Billy and Mandy, thinking Gregory is Grim, take him with them, and eventually return him to his mother, allowing Grim to rejoin the group.

Nergal, a demon originating from Earth's core, returns with a carnival, seeking to make friends. Billy attempts to assist him in forming friendships but Nergal misunderstands the guidance. Upon discovering that Grim was coerced into becoming friends with Billy and Mandy, Nergal resolves to compel the entire world to be his friends by transforming them into dark creatures like himself, ultimately turning Billy, Mandy, Grim, and even the audience into one.

Billy enlists Grim's help to throw a surprise birthday party for Mandy, and Grim agrees reluctantly, assisting in baking a cake while making sure Mandy remains unaware of the plan. When the surprise is revealed, Mandy points out that her actual birthday is five months away, a detail Billy already knew.

Billy and Irwin play the video game *Beasts and Barbarians* for three days straight, prompting Grim to intervene by transporting them into a real-life version of the game. As they progress, Grim escalates the challenges by altering the dangers they face. Ultimately, Billy, Mandy, and Grim escape back home, but Irwin is left behind in the game world.

In an episode where Billy, Mandy, and Grim go on a school trip to a museum, they encounter Hoss Delgado, a self-proclaimed paranormal hunter who initially believes Grim to be a supernatural threat. After a brief confrontation, Delgado realizes he has been tricked by Billy and Mandy, prompting him to give up his pursuit of Grim. The episode concludes with Delgado continuing his own adventures, as he faces off against a werewolf.

In the episode, Grim takes Billy and Mandy to a shopping mall, where he encounters Eris, the goddess of discord, who is more interested in Adonis. Eris invites Mandy to create chaos with her, leading to a prank war between them. In the end, Mandy tricks Eris into thinking Adonis is in a theater, resulting in an accidental kiss between Eris and Grim.

Billy's habit of eating too much junk food leads to him falling ill, so Grim makes a cure using his grandmother's recipe. Instead of healing him, the cure causes a small creature named Yap-yap to grow on Billy's back, who shares his fondness for junk food. After Yap-yap detaches from Billy and tries to avoid an antidote made by Mandy, he eventually ingests it and is destroyed.

Billy turns to Grim for assistance after being repeatedly teased by a bully named Sperg.

Billy becomes possessed after taking an evil book from Grim, which leads him to open a portal in an attempt to summon Yog-Sothoth. Mandy recruits Hoss Delgado to stop him, and the conflict is resolved when Billy is thrown into the portal himself. Moments later, Billy emerges, stating that he was not wanted on the other side.

When Mandy and her family leave for the day, Billy feels lonely, so Grim creates a toy-based imitation of Mandy to keep him company. However, the fake Mandy becomes overly aggressive, frightening Billy. When the real Mandy returns, she accidentally destroys the fake version while playing on the see-saw.

In this episode, Billy befriends a brain-eating meteor that crash-lands in Endsville. He helps it grow by feeding it brains, which eventually leads to the town's inhabitants being turned into zombie-like creatures with glowing green eyes. The episode includes the song "BRAINS!", written by Voltaire, who also provides the voice for the meteor. The story culminates when the meteor consumes Mandy's brain and transforms into a brain-eating version of her.

Billy, Mandy, and Grim eat moldy pizza and fall asleep, each having strange nightmares. Billy's cute bunnies turn into monsters, Grim is haunted by an endless army of authoritative Mandys, and Mandy imagines herself commanding demons in a volcanic landscape similar to *Fantasia*'s "Night on Bald Mountain." Mandy later admits she enjoyed her dream and eats the last slice of the spoiled pizza.