The books in the series:
- Bad Mermaids Make Waves (2017)
- Bad Mermaids: On the Rocks (2018)
- Bad Mermaids: On Thin Ice (2019)
- Bad Mermaids Meet the Sushi Sisters (2020)
Bad Mermaids contains examples of:
- Antagonistic Offspring: In On the Rocks, the human Susan Silkensocks plans to capture mermaids and dig up mermaid buildings to create a tourist attraction. Her first exhibit is going to be Arabella Cod, queen of Hidden Lagoon, whom she is holding prisoner in a tank. When Susan's daughter Paris finds out, she drags Arabella's tank to the beach to free her. Susan travels under the sea in search of more mermaids to imprison, and Paris follows her to foil her plans.
- Appeal to Obscurity: In Bad Mermaids Meet the Sushi Sisters, the spy Meri Pebble is terrified the Sushi Sisters will blow her cover.Meri: Only one spy mermaid has ever failed her first proper mission, and do you know what her name was?
Beattie: Nope.
Meri: Exactly! Because she got kicked out of spy school and never spied again.
Beattie: To be fair, no ordinary mermaid would know the name of any spy - because they're meant to be stealthy and, well, spies.
Meri: Not the point. - Bad Influencer: The Sushi Sisters are famous in the undersea world for their prank videos, but their "pranks" tend to be downright cruel - they shave a mustache whose owner has been growing it his whole life and plan to electrocute a nonviolent shark and slime an old woman. They spend most of the book planning their biggest prank yet: turning Beattie into a half-mermaid, half-sushi.
- Bamboo Technology: Mermaids use TVs, flip phones, and cars made out of clamshells.
- Character Tics: Zelda's left eye twitches when she's about to say something negative.
- Civilized Animal: Steve the sea horse is the only sea creature in Hidden Lagoon who can talk. Beattie's mum, the explorer Belinda Shelton, found him near a shipwreck and took him home as a souvenir. He wears glasses, lives in a pair of dentures, and is obsessed with Hidden Lagoon's most popular cartoon, The Clippee Show.
- Fictional Sport: The most popular sport in Hidden Lagoon is shockey, which is played between two teams consisting of six riders and two swimmers. Swimmers race around a track trying to pass the checkpoint with the shockey pawn, a human shoe. Riders chase after the swimmers and try to stop them, using different sea animals as mounts.
- Frame-Up: In On Thin Ice, Sabrina, the sea horse who teaches at the spy school in Fortress Bay, really wants a sea witch at the school. She frames Gronnyupple for theft so she can offer her a chance to escape prison by working at Fortress Bay.
- Gadgeteer Genius: Paris, who calls herself the Gadget Queen, has built a secret gadget cave under the ice cream stall where she works. Inventions include headphones that let her eavesdrop on conversations on the beach, a hidden camera in Susan's hair that sends a video feed to Paris's hideout and sounds an alarm when she's close by, and tracking devices that she uses to track Beattie, Zelda, and Mimi. Her ice cream stall even converts into a boat that she uses to travel to the Crocodile Kingdom.
- Grass is Greener: So many young mermaids have been wishing for legs that Arabella Cod started an initiative to give mermaids legs so they can spend a summer on land. The vast majority opt to return to the sea once their time is up.
- Harmless Freezing: Gronnyupple catches Susan Silkensocks using a spell that harmlessly freezes her in a block of ice for several minutes. Unfortunately, she catches the Expendable Clone who will disappear in a few minutes anyway. The real Susan is still at large.
- Hide Your Otherness: Inverted in On the Rocks, in which the human Susan Silkensocks passes for mermaid by wearing a fake tail and a breathing device that looks like a thin film over her face.
- I Just Want to Be Special: Steve thinks he's a miracle, the only talking seahorse in the world. In On Thin Ice, he's dismayed to discover Pinkly Lagoon, which is full of talking seahorses.
- Improvised Lockpick: In Bad Mermaids Meet the Sushi Sisters, Steve picks a lock with his tail.
- Incredible Shrinking Man: In On the Rocks, Gronnyupple and Beattie drink a shrinking potion so they can infiltrate the headquarters of Crabagram, the mermaid mail service. Unfortunately, the spell wears off after a few minutes, and the two mermaids are immediately attacked by angry crabs.
- Jet Pack: Some of the sea horses of Rainbow Landing use shell jet packs to get around faster.
- Long-Lost Relative: In On Thin Ice, Steve is reunited with his family in Rainbow Landing: his parents Steven and Stevie and his sister Sabrina. He decides to spend half the year with his family and the other half in Hidden Lagoon.
- Lying Finger Cross: In Bad Mermaids Meet the Sushi Sisters, Zelda makes Beattie promise not to use magic around the Sushi Sisters, even if it looks like they're not looking, because it's too dangerous. Beattie says, 'Promise', while crossing her fingers behind her back.
- Nearly Normal Animal: Old Wonky, an octopus who works as a palace servant, can understand everything mermaids say but can't talk. He can answer yes or no questions by wriggling or rocking. When he tries to say more complicated things, he usually isn't understood, like when he jumps up and down on Liberty Ling's throne to show that she's responsible for fishnapping Arabella Cod.
- Older Than They Look: The powerful witch Maritza Mist is 4,008 years old, but when she was seven she smeared her tail with immortality paste, and now she looks like that age forever.
- Palatial Sandcastle: The rich mermaids of Oysterdale live in giant sandcastles with crystal windows.
- The Password Is Always "Swordfish": The top secret passcode to enter Hidden Lagoon, which no human has been able to guess in thousands of years, is 'Ihavenolegs'.
- Previously on…: On the Rocks and On Thin Ice open with summaries of the previous book.
- A Rare Sentence: In On the Rocks, Zelda complains, 'I did not just get sucked tail-first through a washing machine to be bitten by a fish. And that is a sentence I never thought I'd say.'
- Seashell Bra: Long ago, all mermaids wore shell tops, which are two shells connected by string. Nowadays T-shirts are more common, but shell tops are still fairly popular. Last century there was a fad for shell tops with huge shoulder pads.
- Single-Minded Twins: The Teenies are triplet mermaids who say everything in unison and are never apart, even though they protest that they're actually very different.
- Speaks Fluent Animal: In On the Rocks, Mimi finds out she's a fish talker, which means she can talk to sea creatures other than Steve.
- Themed Party: Mimi and Zelda, who are twins, argue every year about what kind of birthday party to have. Mimi wants a Clippee-themed party. Zelda wants a birthday-themed party.
- They Called Me Mad!: Susan has been trying to prove the existence of mermaids for years. She even wrote a book called It Had a Tail (Stop Calling Me a Liar). She plans to capture mermaids and dig up mermaid buildings to use in a tourist attraction.
- Tyrant Takes the Helm: In Bad Mermaids Make Waves, Arabella Cod is fishnapped and imprisoned in a tank on land. Hidden Lagoon is taken over by a mysterious mermaid named The Swan who keeps everyone under lockdown and forces them to spend all their time making shell tops. The only mermaids who can do what they want are the mermaids of Oysterdale, who are allowed to loot the other cities. The Swan turns out to be a puppet of her "henchman" Ommy Pike, who plans to force everyone to wear shell tops so he can mind control them using the Ruster Shells, a magic shell top that only works on people who are dressed the same. He allowed the looting because he wants to live in Oysterdale, and theft is an easy way to get people to move all the nice things from the other cities to Oysterdale.
- Underground City: Salmon City, a mermaid city off the coast of Greenland, consists mostly of pebble houses in a cave under the seabed. Its entrance is hidden by an old shipwreck.
- Underwater City: There are five cities in Hidden Lagoon: Swirlyshell, the largest city, where the buildings resemble giant spiral shells; Oysterdale, where the richest mermaids live; Hammerhead Heights, which is located in a canyon and is inhabited by both shark mermaids and actual sharks; Anchor Rock, which is smaller and colder than the other cities and decorated with shipwrecks and human trash; and Lobstertown, home of Clawacana Stadium and Hidden Lagoon's most successful shockey team. There's also the Kelp Forest, a trendy suburb of Hammerhead Heights whose economy is based on kelp products.
- Unscaled Merfolk: The mermaids of Lobstertown have lobster tails, while the ones from Hammerhead Heights have shark tails. In later books, the protagonists learn about Frostopian mermaids with orca tails and Octopollian mermaids with octopus tentacles.
- Voluntary Shapeshifting: When Paris frees Arabella, Arabella gives her a magic necklace that can transform her into a mermaid, a crocodile, a jellyfish, a shark, a lobster, a fish, a dolphin, or back into a human if she shakes it the right number of times.
