Sweet Mayhem and Queen Watevra's Mishap Adventures is a custom Lego movie. It focuses on the mini-doll/shapeshifter duo Sweet Mayhem and Queen Watevra Wa'Nabi and their escapades taking place during the events of Unikitty!, The Lego Movie, The Lego Batman Movie and The Lego Movie 2: The Second Part. Much of the original cast from the first movie, Unikitty!, The Lego Batman Movie and The Lego Movie 2: The Second Part return in this custom film to reprise their roles, including Stephanie Beatriz and Tiffany Haddish as Sweet Mayhem and Queen Watevra Wa'Nabi, respectively.
As Sweet Mayhem and Queen Watevra Wa'Nabi watch The Lego Movie in a theater, Sweet Mayhem decides to fast-forward to their scenes in the second movie. Queen Watevra's protest over this eventually prompts Sweet Mayhem to share her backstory, going back to before the beginning of the movies.
Sweet Mayhem is a social outcast in his mini-doll friends and family at Heartlake City due to frequently messing things up by accident. Though she is unconditionally supported by her mother, Anna, Sweet Mayhem dreams for more in life than her friends' bleak existence hiding from dinosaurs. One day, she is assigned as a sentry, but her daydreaming nearly leads to the near-death of his father, Peter by velociraptors Rocky, Conner and The Other One. This becomes the last straw for the mini-dolls, prompting Sweet Mayhem to leave and to find a better life. She meets Balthazar, who teaches her about "Super Cool" and advises her to "look beyond what you see". Sweet Mayhem takes the advice literally and observes Unikingdom in the distance. Believing Unikingdom to be her paradise home, Sweet Mayhem ventures there and encounters Watevra Wa'Nabi on her way. The two quickly form a bond and Watevra accompanies Sweet Mayhem.
The pair arrive at Unikingdom during the presentation of Unikitty and Puppycorn to the Unikingdom's residents. As they make their way through the crowd of onlookers, Watevra explosively passes gas, causing nearby residents to faint but prompting residents further away to bow to Unikitty and Puppycorn. Following this, Sweet Mayhem and Watevra make multiple attempts to set up homes throughout the brick world, but wind up being forced away every time after witnessing several events from Unikitty!, The Lego Movie and The Lego Batman Movie, such as Unikitty singing "Catchy Song", Emmet, Lucy and Vitruvius escape from Bad Cop and the robots, and Joker's conspiring with the villains. Eventually, the pair are caught in the attack that destroys Cloud Cuckoo Land in the original film, and are thrown off a waterfall. Exhausted, Sweet Mayhem decides to give up, until Watevra discovers a luxurious palace in Space. The pair finally settle there with the philosophy of "Super Cool".
Eventually, Sweet Mayhem and Queen Watevra encounter baby Susan in a nearby desert, nearly dead. The pair rescue her and decide to raise her under their philosophy. After the events of The Lego Batman Movie, Batgirl appears after chasing Queen Watevra and reunites with Batman. Believing "Super Cool" to be in jeopardy, Sweet Mayhem and Queen Watevra attempt to sabotage their dates, but fail. After witnessing Batman and Batgirl's argument, Batman disappears. Five years later, Lucy explains that Emmet has to challenge Rex Dangervest, and that they need their help. Hurt that Emmet left them, Sweet Mayhem unsuccessfully tries to persuade Queen Watevra to stay, but Queen Watevra follows Lucy instead. Sweet Mayhem indulges in the Palace' luxuries by herself, but loneliness starts to overcome her. Balthazar appears again and helps Sweet Mayhem realize that her true Super Cool is with the ones she loves, prompting Sweet Mayhem to take off after Lucy and Queen Watevra.
Sweet Mayhem catches up and reconciles with Queen Watevra, before they journey onward to save Emmet. After helping Lucy distract the velociraptors, Sweet Mayhem and Queen Watevra run into Anna and Peter, who came looking for Sweet Mayhem. Sweet Mayhem proposes that they all help Emmet by getting rid of the velociraptors. Whilst Emmet and Lucy battle Rex, Anna and Peter are directed to construct a series of tunnels beneath the velociraptors, and Sweet Mayhem and Queen Watevra use various tactics to distract them while the tunnel is being made. When the tunnels are finished, Peter knocks down the sticks, breaking the ground under the velociraptors. However, the last few get stuck, prompting Sweet Mayhem to dive underground and break them himself. The cave-in commences, and the velociraptors are ejected through the tunnels. Immediately afterwards, Rex is defeated by Emmet and Lucy. Emmet accepts his place as hero of Syspocalypstar, thanking Sweet Mayhem and Queen Watevra for helping him. Sweet Mayhem takes Anna, Peter, and the mini-dolls to live in the velociraptor-free palace to complete her "Super Cool"; and she is praised as their hero.
Once Sweet Mayhem finishes her backstory, Anna, Peter, Emmet, Lucy, Susan, Balthazar, and eventually many other LEGO characters join her and Queen Watevra to rewatch the film in the theater in which Queen Watevra tells Sweet Mayhem that she still doesn't do well in crowds.
- Stephanie Beatriz as Sweet Mayhem
- Tiffany Haddish as Queen Watevra Wa'Nabi
- Chris Pratt as Emmet and Rex Dangervest
- Elizabeth Banks as Lucy
- Jenny Slate and Kath Soucie as Susan (Kath Soucie voices baby and young Susan)
- Jill Talley as Anna, Sweet Mayhem's mother
- Tom Kenny as Peter, Sweet Mayhem's father
- Arnold Schwarzenegger, Sylvester Stallone and Frank Welker as Conner, Rocky and The Other One
- Noel Fielding as Balthazar
- Will Arnett as Batman
- Alison Brie as Unikitty
- Grey DeLisle as Puppycorn
- Roger Craig Smith as Hawkodile and Richard
- Kate Micucci as Dr. Fox
At the ending, while the film is rewinding back to the beginning, silhouettes of the following Lego characters join Sweet Mayhem, Queen Watevra Wa'Nabi, Anna, Peter, Emmet, Lucy, Susan and Balthazar in the audience:
- SpongeBob SquarePants
- Wonder Woman, Harley Quinn, Batgirl, Supergirl, Poison Ivy, Bumblebee, Lena Luthor and Lashina from DC Super Hero Girls
- Bad Cop and President Business from The Lego Movie
- Robin, Alfred and Joker from The Lego Batman Movie
- Lloyd and Master Wu from The Lego Ninjago Movie
- Forky, Woody (2010), Bo Peep, Buzz Lightyear (2010), Jessie (2010), Ducky and Bunny from Toy Story
- Olivia, Emma, Stephanie, Mia and Andrea from Lego Friends
- Lightning McQueen and Mater from Cars
- Ice Cream Guy, Bananar, Tempo, Melody-Melody, Chocolate Bar Guy and Royal Guard from The Lego Movie 2
- Tom Hanks as Woody (2010)
- Annie Potts as Bo Peep (mini-doll)
- Tony Hale as Forky
- Tim Allen as Buzz Lightyear (2010)
- Joan Cusack as Jessie (2010)
- Keegan-Michael Key and Jordan Peele as Ducky and Bunny
- Grey DeLisle as Wonder Woman (mini-doll)
- Tara Strong as Harley Quinn and Poison Ivy (mini-doll)
- Ashlyn Selich as Batgirl (mini-doll)
- Anais Fairweather as Supergirl (mini-doll)
- Teala Dunn as Bumblebee (mini-doll)
- Romi Dames as Lena Luthor (mini-doll)
- Jessica DiCicco as Lashina (mini-doll)
- Owen Wilson as Lightning McQueen (2011)
- Larry the Cable Guy as Mater (2011)
- The film reveals the story of Sweet Mayhem's origin and how she and Queen Watevra first met each other and became friends.
- Sweet Mayhem has her helmet off the whole movie.
- Queen Watevra doesn't shape-shift in this film for some reason.
- The Film's script and plot are a spoof of The Lion King 1 1/2.
- Sweet Mayhem has all of Timon's places, moves and lines.
- Queen Watevra Wa'Nabi has all of Pumbaa's places, moves and lines.
- Anna has all of Ma's places, moves and lines.
- Peter has all of Uncle Max' places, moves and lines.
- Conner, Rocky and The Other One have all of Shenzi, Banzai and Ed's places, moves and lines.
- Balthazar has all of Rafiki's places, moves and lines.