Literature: Percy Jackson and the Olympians aka: Percy Jackson
If you're a normal kid, reading this because you think it's fiction, great. Read on. I envy you for being able to believe that none of this ever happened. But if you recognize yourself in these pages-if you feel something stirring inside- stop reading immediately. You might be one of us. And once you know that, it's only a matter of time before they sense it too, and they'll come for you.
Percy Jackson and the Olympians is an Urban Fantasy series by Rick Riordan based on Greek mythology. The Sequel Series, The Heroes of Olympus, has its own page. Its first four books,The Lost Hero, The Son of Neptune, The Mark of Athena, and The House of Hades, have already been released. The first two book movies, Percy Jackson & the Olympians: The Lightning Thief, and Percy Jackson: Sea of Monsters have been released.In the books the Greek gods have moved to the United States, and their home, Olympus, is now located at the 600th floor of the Empire State Building. They have many demigod children with mortal humans. Unfortunately, these demigods attract mythological monsters, so they must travel to a safe haven in Long Island, New York, called "Camp Half-Blood", and learn to fight. The books get progressively Darker and Edgier throughout the series as a war with the Titans approaches.The books in the main series are:
The Lightning Thief
The Sea of Monsters
The Titan's Curse
The Battle of the Labyrinth
The Last Olympian
There are also four companion books:
The Demigod Files: Includes three short stories and information about Camp Half-Blood.
The Ultimate Guide
Demigods and Monsters
The Demigod Diaries: Includes three additional short stories as well as a short story by Rick Riordan's son, Haley
Abusive Parents: Many gods neglect their children. It's the biggest reason why there is a Titan army. There are kids who are never claimed. They get stuck at the Hermes cabin.
Nemesis, God of Balance and Revenge, to Ethan. The one time they meet, she blinds his left eye with the promise that he would bring balance to the world once again.
You've got Kronos, Father of the gods, who ate his own children to keep them from rebelling against him.
In the first book, Percy's stepfather, "Smelly" Gabe, treats both Percy and his mom like dirt. Thankfully, Sally Jackson uses the Medusa head from Percy on Gabe, sells the statue, and gains enough money from it to go into writing.
Actually, in the last book, there's a scene where the Titan army is at Medusa's "garden gnome" shop and it describes how some of the statues (including one that used to be Grover's Uncle Ferdinand) are broken, but there's no indication that the break did anything to "release" the person or creature from the stone prison, so it would appear that once they've been turned to stone, there's no coming back and - for all intents and purposes - they are dead.
Achilles' Heel: Figuratively and literally. Taking a dip into the River Styx enables you to become invincible so no weapon will harm you, except at a tiny spot somewhere on your body. Along with Achilles' actual heel, the final book has two—a spot on Percy's back and a spot near Luke's armpit. Additionally, the tiny weak spot isn't the only Achilles' Heel of taking a bath in the Styx. While you Take a Level in Badass in addition to becoming invincible, you do so basically by turning your body Up to Eleven, meaning you need especially long periods of rest in-between fights. Meaning that if someone throws enough Mooks at you, you will drop from exhaustion faster than a normal person.
In addition, it is implied that bathing in the Styx amplifies the bather's own personal "fatal flaw"—you become heavy with one emotion (such as pride) that can be used against you. This is somewhat subverted in that the weakness that Percy has, personal loyalty, doesn't actually link in to a defeat in the finale.
Action Girl: Tons. Annabeth, Thalia, Bianca and Zoe to name a few. Just as helpful as the boys, usually.
Affably Evil: Geryon. He makes omelettes from the eggs of endangered species, slaughters the cattle of the sun, sells to Kronos' army, and enslaves Nico. On the other hand, he doesn't interfere with quests, holds barbecues for his captives, and gives people a grand tour of his ranch.
A Form You Are Comfortable With: Most of the Gods and Goddesses upon their first appearances. Occasionally subverted when they decide to show their true forms, but Percy usually doesn't look when they do this.
All Myths Are True: If it showed up in any Greek mythological story, it's not a myth. And it probably wants to kill you. When Percy asks about whether or not God exists in the first book, he's told by Chiron that he would be getting "metaphysical". Apparently the Olympians don't know if He exists any more than we do.
The Kane Chronicles, the other YA Fiction series by Rick Riordan actually taking this a step further, suggesting not only that all Greek myths are true (the series ties in to the Percy Jackson series) but by also stating all Egyptian gods are real. Moses of the Abrahamic religions is also mentioned.
The Kane Chronicles had a line about the Faust Family being deeply involved with supernatural whatsits as well, so it can be assumed European fairy tales might just be fair game as well.
Dionysus playing Pac-Man: The world will fall, the gods will die, and I will never achieve a perfect score on this stupid machine!
The punishments in the Underworld:
"Even from far away, I could see people being chased by hellhounds, burned at the stake, forced to run naked through cactus patches or listen to opera music."
That depends: there is some opera that might be truly dreadful to listen to.
Ascended Extra: Hestia, who appears in the first book stoking the campfire at Camp Half-Blood, but Percy doesn't find this out until The Last Olympian.
Attention Deficit... Ooh, Shiny!: All demigods have ADHD, which is a sign of their battlefield reflexes and greater sensory perception. The disorder is handled well, though, since Riordan's son has ADHD and he knows what he's talking about.
Attending Your Own Funeral: Percy is launched out of a forge in Mount Saint Helens in Battle of the Labyrinth and wakes up on Calypso's island. He spends the equivalent of two weeks there. Hephaestus then enchants a raft that allows Percy to drift back to Camp Half-Blood. When he arrives, he walks in on his own funeral as the campers prepare to torch his shroud.
Author Avatar: Percy is basically the representation of the author's son who has ADHD and dyslexia. It seems the gods do as well.
Oh, and by the way, Edward Teach (also known as Blackbeard) is a son of Ares. He and his crew have been trapped in Circe's cage as guinea pigs for about 300 years, so when they are turned back into humans by Percy's vitamin pill, they take no hesitation in ransacking the isle as revenge.
The Bermuda Triangle: With mythological sites that used to be around Greece and Rome now located in America, this location got to take the title of the Sea of Monsters from the Mediterranean Sea.
Best Her to Bed Her: This seems to be how romance works at Camp Halfblood: "If a girl keeps trying to kill you it means she's into you."
Betty and Veronica: Subverted with Annabeth and Rachel; both are very nice girls who like Percy (the Archie). If one had to get technical, either one could be considered the Betty or the Veronica; Annabeth could be the Veronica, since she's meaner and more violent (but not terribly) than Rachel, who is almost always polite and well-mannered (since she's from upper class) and because of that could be considered the Betty. Or one could consider Annabeth to be the Betty, since she's known Percy for longer, is best friends with him, and is blonde, while Rachel, in true Veronica fashion, becomes friends with Percy later on and interferes in Percy and Annabeth's budding romantic relationship, albeit unintentionally. Both girls are considered to be very good-looking by others, furthering the justification.
Big Applesauce: It's where Mount Olympus is located, and Percy's home town.
Blessed with Suck / Cursed with Awesome: Having a perfect understanding of ancient Greek, and whether you are willing to tolerate having ADHD as a side effect of your supernatural combat instincts. And then there's all the monsters you attract, especially if you carry a cell phone
Grover has managed to locate half-bloods on three separate occasions. Unfortunately, all of them have been children of the Big Three, and thus the most likely to die.
Broken Bridge: Inverted. In the fifth book, Percy destroys the Williamsburg Bridge in an attempt to stop Kronos's army.
Butt Monkey: Humanity in-universe, or at the very least Westerners. Whether it's tourists being turned to stone by Medusa, children being lured into a Lotus-Eater Machine for eternity, or innocent shoppers being stretched to death or hacked up by Procrustes, it sucketh verily to be a human in the Percy Jackson universe.
And if humans are lucky enough to avoid those fates, then they usually end up being the innocent victims of divine temper-tantrums, cosmic playthings for the gods, and in general are oblivious to the world around them.
Camp Unsafe Isn't Safe Anymore: In the second Percy Jackson book, Percy Jackson and the Sea of Monsters, Camp Half Blood is "no longer safe" because someone has poisoned Thalia's pine tree, which usually keeps the camp safe from outside monsters. However, the camp was never safe from anyone on the inside who wanted to hurt anyone else on the inside, as demonstrated by the ending of the first book.
Cannot Spit It Out: A staple of the series; if anyone has any sort of vital information, they will hold it back for longer than necessary. Most often they have their reasons for it, but it still gets very noticeable after a few books. And when they do try to tell straight away, they're generally interrupted by someone or something else before they can get to the point. Of course, this is based on Greek mythology so it's not surprising.
Celestial Bureaucracy: The Underworld, all the way. You know the Ancient Greek tradition of putting a coin in the dead's mouth to help them pay their passage across the River Styx? Charon charges people's credit cards. And if you're a kid and don't have one? Well, you're kind of screwed.
Messed with in the movie. Charon takes drachma like in the original myths. When Grover tries to pay him with U.S dollars, he BURNS THE MONEY. The scene is even complete with a recession joke.
Chekhov's Gunman: Remember Circe's assistant in The Sea Of Monsters? Now read the second book of the second series. Also, that little girl at the campfire in the very first book turned out to be rather important...
Circles of Hell: What did you expect? This is Greek mythology. Within the Underworld, there's the Isles of the Blest at the top, Elysium below that (or encircling them), the most widely populated Asphodel Fields, and then the Fields of Punishment.
Then there's also the fact that you get special punishment from Hades himself if you're sufficiently bad.
It's implied your soul get's sewn into his clothes a little bit later.
Cool Sword: Riptide and Backbiter. Also Nico's sword made out of Stygian iron.
Cool and Unusual Punishment: Percy mentions being forced to listen to opera music for eternity as one of the tortures inflicted in the Fields of Punishment.
Corrupt Hick / Corrupt Corporate Executive: Geryon makes omelettes out of the eggs of endangered species, slaughters the sacred sun cattle, has contracts to the Titan army, and tries to sell Nico to Luke.
Corrupt Corporate Executive: One of the spirits that Percy, Annabeth and Grover see getting stopped by a security guard at the Underworld security checkpoint in the first book is one that Percy recognizes as a televangelist who had promised to raise millions of dollars for orphanages....but was then caught embezzling it and pocketing it for himself to spend on his own mansion. He was then killed in a police chase after his Lamborghini for the Lord ran off a cliff.
Creator Provincialism: The United States is literally the current center of western civilization. Canada is mentioned, but only because it's where Laystrigonian giants are from.
In the sequel, Canada is featured more.
Crossover Cosmology: The Roman god Janus appears in the fourth book. Word of God said in an interview that the Roman gods exist but they are younger than the Greek gods. Riordan's other novel series, The Kane Chronicles, which features Egyptian gods, also takes place in the same universe.
The Heroes of Olympus takes this a step further, suggesting that the gods do go around in their Roman aspects and there is an opposite camp for their children.
The camp is either Camp Jupiter or New Rome, depending on who talks about it. Percy gets sent there with God-Guided Amnesia as an unwilling participant of Hera trying to the two together. Also, the gods morph depending on who's talking to them (Zeus for a Greek, Jupiter for a Roman). Unless the two sides are in a war, then the gods are debilitated and constantly switching between the two forms.
Cruel and Unusual Death: Bianca is electrocuted inside a giant bronze automaton in New Mexico. Zoe is killed by a combination of dragon poison and her father on Mount Tamalpais. But the laurels definitely go to Silena, who's facially disfigured by the acid breath of a giant, two-hundred-foot-long worm that and gets launched into the pavement.
Silena's death doubles as Fridge Horror when you think about whose child she is. A daughter of Aphrodite essentially having her face melted with acid? That would be like Annabeth losing all of her intelligence and dying because of it. Or Percy drowning and dying!
Crystal Dragon Jesus: Consciously averted. Percy initially equates the concepts of God and the Greek gods, but Chiron is quick to point out that God is "metaphysical" and therefore in a different category from the Olympians.
Cue the Flying Pigs: A particularly dangerous one is the Clazmonian Sow who lives around Cloudcroft, New Mexico.
Darker and Edgier: The series gets progressively darker with each following book, finally capping off with the deaths of Silena, Beckendorf, Luke and more and quite a few tearjerkers in The Last Olympian.
Dark Secret: Zoe is the daughter of a titan general, Kronos' right hand. Also she was the mastermind behind at least one of "Hercules'" great victories; it's implied she may have helped him with others.
Deadpan Snarker: Pretty much everyone is a deadpan snarker (though Percy probably gets the most in). The chapter titles are almost always deadpan snark in some way: "I Accidentally Blow Up My Pre-Algebra Teacher" is the first.
Despair Event Horizon: Percy has one in The Last Olympian when Silena diesafter revealing she was The Mole, Rachel cuts him off, Annabeth is angry at him over Luke and Rachel, his parents are caught in the cursed sleep, Olympus seems about to fall, and he'd seen the cruel acts of Zeus, Hades, and Hermes. He almost lets Hope out of Pandora's Box and surrenders, but after remembering some inspiring words from Chris Rodriguez and Nico, he instead gives the jar to Hestia and fights on stronger than ever.
Does This Remind You of Anything?: Percy says he is expecting the Underworld entrance to be pearly gates or a black portcullis. The actual result is...an airport security checkpoint. There's an EZ Death line, as well as two Attendant on Duty lines that crawl at a very slow rate. Also, the spirits in the waiting room have been there for a few hundred years.
Doomy Dooms of Doom: Chapter 14 in the second book is titled "We Meet the Sheep of Doom" on Polyphemus's island. These are sheep who rush and kill a poor defenseless deer right in front of Percy and Annabeth. A deer who goes from being a living creature to being a pile of bones picked entirely clean in under two seconds.
Down in the Dumps: In book three, Percy and crew wander into the "junkyard of the gods" in Yuma Claw, Arizona and end up setting off a giant automaton. Naturally.
This is sort of subverted in the fifth book where it's explained that gods have no DNA so it's totally not creepy for half-bloods from different god parents to date, like Silena Beauregard to Charles Beckendorf. They do specify that two demigods from the same parent (a son and daughter of Athena, for example) would never ever consider dating.
Everything Makes a Mushroom: In the second book, Tyson and Percy, playing with chemicals, make a "miniature mushroom cloud" near the trash can.
Yes, but Tyson is a Cyclopes (and good at crafting), so for all we know he was playing with depleted uranium or somesuch.
Everything's Better with Rainbows: The ever-handy Iris message. It requires water vapor spray to create a rainbow, so artificial sources are used: in The Lightning Thief, when Percy, Grover and Annabeth are in Denver and contacting Luke at camp, they utilize the spray machine of a self-service car wash. In The Sea of Monsters, the wake kicked up by Percy and Annabeth's lifeboat allows them to create an Iris message intended to go to Chiron, who unfortunately is in the middle of a noisy party, leading to the communication breaking up. Starting in the third book, Percy has a special fountain in his cabin with gold drachmas at the bottom that allow him to communicate with others when necessary.
They don't like cell phones because monsters can easily trace them.
Fail O'Suckyname: Gabe Ugliano? Keeping a rebellious streak aside, there's absolutely no way Percy's mom would have sacrificed her maiden name for that surname. Good thing he gets what's coming to him at the end.
Fatal Flaw: Played straight with Annabeth, Percy, and the entire Hades bloodline. Played with in that Athena points out Percy's fatal flaw, but it never ends up being used effectively against him.
Actually, it does get used against him, quite effectively. Just, never after Athena tells him about it, which may be in part due to Kronos' titanic ego and the fact that they're at war from the point he finds out.
While it's not used directly against him per se, we do frequently see Percy get reminded during TLO to stop trying to fight every single battle and save everyone himself, since he'd wear himself into the ground that way. It may not have been mentioned by name, but it's still present.
In The Kane Chronicles we finally find out why: they're being banished to the deeper regions of the underworld, and it takes them awhile to claw their way back out.
And in the newest series, something has happened in the underworld that lets monsters (and the dead) return to earth with relative ease. May, or may not, be related to the events in The Kane Chronicles.
Nope, it's because Gaea opened the gates of Tartarus.
Fix Fic: The series has a staggering amount of these, almost all of them either regarding Luke and un-killing him, Thalia and her quitting the hunters in order to be able to be romantically involved, or Rachel Elizabeth Dare being able to date someone even though she too cannot become romantically involved.
Flirty Step Siblings: A really loose example, but Silena, Aphrodite's daughter, and Beckendorf, Hephaestus' son, are technically step-siblings, seeing as their divine parents are married.
While accurate it should be pointed out that Hephaestus and Aphrodite were an arranged marriage. Most myths state that Zeus had Aphrodite marry Hephaestus so that she would stop causing so many problems with the other male gods and he felt Hephaestus was a person of good character who would be a good husband. While true Hephaestus was also, unfortunately, rather ugly so Aphrodite had NUMEROUS infidelities.
In other stories Hephaestus knew what he was getting into and had a good sense of humor about it, hence his prank booby traps of epic proportions.
Probably accidental, but Hyperion is pretty much this for Hades - one is a god and the other is a titan, Dark Is Not Evil vs Light Is Not Good, and both their names start with "H".
Luke for Percy.
Freudian Excuse: Some of the half-bloods blame their parents for not loving them, abandoning them, etc. and use this as their excuse for joining Kronos's "dark side".
Gas Leak Coverup: At the start of The Sea of Monsters, when the Laistrygonians firebomb the gym in their attempt on Percy's life, Percy, Annabeth and Tyson quickly flee because they're certain they're wanted by the police. At the end of the story, when the quest is over, Chiron tells Percy that he convinced the school officials that the bombing was not his fault, by manipulating the Mist to make them think it was just a very badly timed furnace explosion. Percy is still expelled for "ungroovy karma".
Genre Blindness: Percy has an absolutely terrible track record in terms of recognizing the various mythic monsters and traps he stumbles across, even though most of them are obvious variations on well-known episodes from things like The Odyssey. Occassionally, he is Genre Savvy - In The Sea of Monsters knows Tantalus's background upon first meeting him at Camp Half-Blood. He knows about the Sirens when he and Annabeth encounter them, and the dangers they pose. And in the first book, he knows Procrustes' background.
Lampshaded once when Percy mentions that they should know they are walking into a trap but after walking for hours, not eating, and craving a bed to sleep on they tend to do stupid things.
By the time Labyrinth rolls around, they're more or less Genre Savvy, whereupon the universe actually starts changing the rules just to throw them off.
Getting Crap Past the Radar: Seriously, of all the ways for Mr. D to get Percy's name wrong, his favorite is Peter Johnson? Especially given the reputation of his followers, back in the day...
The series never outright calls any of the demigods illegitimate, though at one point Hera calls Percy "one of Poseidon's...children," and Percy knows she definitely implied something else, like "mistakes".
In the movie, Persephone hates Hades so much she has "visitors" every once in a while. You know, lovers. When she comes across Grover, she says, "I haven't had a satyr... visit before." Moreover...
Also in the movie, Medusa tells Percy "I used to date your daddy." Any Greek mythology student will tell you it was more like a one-night stand. A non-consensual one-night stand.
In The Titan's Curse, Percy, Thalia, Grover and Zoe Nightshade arrive at Hoover Dam, causing a hurricane of DAM[N] jokes:
Zoë Nightshade: "Let us find the dam snack bar."
Grover Underwood [smiling]: "The dam snack bar?"
Zoë Nightshade: "Yes. What is funny?"
Grover Underwood [trying not to laugh] "Nothing, I could use some dam french fries."
At the meeting with Hyperion, Thalia tells him "That's a load of Minotaur dung." Given that minotaurs are half bull, and "dung" is another word for "shit"...
The fact that Chiron and Mr. D are running the camp arguably counts, given that Dionysus was eromenos to Chiron in some stories, and apparently learned "the bacchic rites" from him.
Ganymede is mentioned in the second book, where he says he always buckles up in a recorded safety spiel in the Gray Sisters' Taxicab. His special relationship with Zeus isn't.
In the 'Sea of Monsters' movie, Polyphemous laments being forced to eat his sheep. Wait. If they weren't already there for eating, what were they there for? And was he wearing a kilt?
The 'Honeymoon Special' waterbed in Crusty's Water Bed Palace has dynamic stabilizers to stop wave motion 'wink,wink,nudge,nudge'.
There's an awful lot of dancing around the conditions for who can or can't be the Oracle in The Last Olympian. It's stated that Maria Castellan had major problems with it because she had... already had children. When Rachel becomes the new Oracle, they note that she won't be dating anyone anytime soon. If you're familiar with Greek mythology, you know that the Oracle had to be a virgin female.
God: Mentioned in The Lightning Thief during a handwave by Chiron.
Chiron: God capital "G" God is something else entirely. We won't delve into the metaphysical.
Godly Sidestep: Soon after Percy learns about the gods, he asks the obvious question and is informed that the gods are "the lower-case 'g' kind" and they "don't deal in metaphysics." Yes, whether or not He exists is something Olympians don't want to investigate.
In The Kane Chronicles, the Egyptian gods of the same universe state that they do not demand worship because, while they are primordial forces, they are still created beings. That poses some interesting questions in light of Chiron's statement on the matter....
Gods Need Prayer Badly: Averted, except in the case of Pan. The belief of the Satyrs, Dryads, and other nature spirits are what have kept him from fading away.
Actually played straight - they just don't need prayer directly so much as people indirectly invoking them. Ex: Dionysus is invoked anytime someone has a party. But it is a rare example of there being a backlash effect: The death of a god harms what they are god of, like Pan and the wild.
Kronos regains a little bit of his power every time a half-blood joins his army.
Another example potentially can be found in that they basically say Apollo and Helios had their roles merged 'because' the Romans merged the two gods.
Good Is Not Nice: Let's be honest, the gods are complete assholes. Their pettiness and vanity often ends up nearly getting the heroes killed, even when they're trying to save the day. Lampshaded by Calypso when she questions Percy on his loyalty to the gods.
Calypso: “Tell me Percy. I have no wish to argue with you. But do you support the gods because they are good, or because they are your family?”
Gray Eyes: The entire Athena cabin (most notably Annabeth), along with the goddess herself. When Percy notices the gray eyes on the tour guide at Hoover Dam in The Titan's Curse, he realizes it was probably Athena disguised.
Green Aesop: Various sea and river creatures get uppity around water pollution, and the quest for Pan eventually turns out to be all about the current state of the environment; this one is extremely well-done, though.
Half-Human Hybrid: The Minotaur is just one of the first examples. There are numerous others that number so many we would be tracked down if their names were posted here.
The Hero Dies: Played straight, and yet not, in that the hero was not who we all thought he was.)
Heroic Bastard: All of the half-bloods, of course, with the possible exception of Athena's children (it depends on whether you can consider children born from thoughts bastards or not). Despite this, the B-word is never outright mentioned, although Hera alludes to it at one point.
Hidden in Plain Sight: Labyrinth entrances. There is one inside Alcatraz. Also, you can find one on the North Shore of Long Island at some ordinary strawberry farm, and at the Times Square Marriott.
If you want to go to Mount Olympus, go to the Empire State Building and get a special card for access to the 600th floor.
The Underworld entrance - DOA Recording Studios in the book, and underneath the Hollywood Sign in the film.
You should never venture near Mount Tamalpais if you are visiting San Francisco. Although in reality there is a weather station up there, there are a lot of very supernatural things going on around there.
Hades causes an earthquake in Los Angeles, which implies that he probably also caused the Northridge earthquake of 1994, the San Francisco earthquake of 1906 and the Loma Prieta quake of 1989.
Edward Teach, Blackbeard, was a son of Ares. And he was not killed in battle with Virginia soldiers. Rather, the soldiers captured him and handed him over to Circe, who transformed him and his crew into guinea pigs.
Hope Spot: Literally in The Last Olympian when Percy gives Pandora's Box to Hestia, and the warmth of her hearth fires inspires him to keep fighting. And despite more bad developments which happen after this, it isn't dashed since they do win.
Humans Are the Real Monsters: Grover and the other satyrs believe this, given their belief that humans mistreated the earth following the death of Pan. Grover goes so far as to play a version of Deer Hunter...where the deer shoot humans, and he laughs gleefully while they do so. Even Hades, the Lord of the freakin' Dead, thinks this, as the events of the 20th-century led to overcrowding in the Underworld even though those events were caused by squabbling demigods, not humans. Percy also shows shades of this at first, given that he's dealt with nothing but bullies and his abusive step-father for his whole life. He grows out of this over the course of the first book however, growing to care for the safety of an innocent family and seeing his step-father as one of the worst examples of humanity rather than being par for the course.
We Are Morons: Given the setting, the vast majority of humans come off as this, incapable of accomplishing anything greater than desk-jockeying without divine parentage.
Humans Are Special: Most aren't particularly notable, but a few of us have traits (i.e., a high level of creativity, stunning looks, above-average intelligence) that make us desirable to the gods. YMMV on if that's a good thing, especially given Zeus' way of...erm, treating those he takes a shine to.
Human Mom, Non-human Dad: Percy, Clarisse, Thalia, and Luke fit under this category, being the children of male gods. Reverse with Silena Beauregard and Annabeth.
Hybrid Power: Demigods are often chosen by the gods to do their work because being half-god and half-mortal, they straddle both worlds and can go places and do things that either mortals or gods cannot.
I Cannot Self-Terminate: Luke needs to destroy himself to defeat Kronos, but can't do it without Percy giving him Annabeth's knife.
Iconic Sequel Character: Thalia Grace does not appear until the very end of The Sea of Monsters and doesn't do anything until The Titan's Curse, but became extremely popular with the fanbase. Her connection with one of the primary characters of the Sequel Series The Heroes of Olympus solidified her importance.
Ditto Nico di Angelo, who first appears in The Titan's Curse and becomes a major player in The Battle of the Labyrinth and The Last Olympian. And like Thalia, he has a connection to one of the main characters of Heroes of Olympus.
Idiot Hero: Percy is… not exactly the sharpest blade on the weapons rack.
I Found You Like This: Percy collapses after fighting the Minotaur outside of Camp Half-Blood. After winning the fight, he awakens inside the camp being tended to by Annabeth Chase.
Percy's arrival at Calypso's island in Battle of the Labyrinth. He passes out while being catapulted out of Mount St. Helens, and when he wakes up, Calypso is treating him.
I Gave My Word: An oath on the River Styx is magically binding. Unless you are a god.
Gods are supposed to be bound by it as well and if they break their word exiled from Olympus for a decade without receiving any divine food. Of course, Zeus being the god in charge of enforcing oaths and not exactly a great role model he decided to not enforce the consequences on himself and the same with Poseidon.
Tyson: I need to go... um... polish my fish ponies.
Inferred Survival: Even after the climax, it's revealed that Kronos is still out there somewhere, as he is immortal and cannot die. It is said that Kronos might be scattered so thin across the world that he might not be able to form a consciousness again, but what would be the fun in that coming true?
Innocently Insensitive: Perdix, it is not a good idea to ask your uncle Daedalus if his son died flying because the wings he made him failed.
Jedi Mind Trick: Or as we should call it here, Manipulating the Mist. Thalia uses it in The Titan's Curse to trick Dr. Thorn and another teacher into thinking that she, Percy and Annabeth are Westover students and not visitors on a rescue mission.
Jerkass: Gabe Ugliano. Good thing it's implied Sally turned him into a statue with Medusa's head. He deserved the comeuppance.
Annabeth, Thalia and Clarisse have shades of this in different books.
Jerk Jock: The Ares Cabin in general, and Clarisse in particular.
Just Train Wrong: There are a couple of glaring instances when it comes to railroads being used in the stories.
For instance, in The Lightning Thief, Percy, Annabeth and Grover take an Amtrak train from New Jersey to Denver, Colorado - a one-seat ride that also goes through St. Louis (for the Echidna encounter in the Arch). There are several things that are extremely inaccurate with their journey:
A one seat ride from New Jersey to Denver via St. Louis is impossible. There are no coast-to-coast intercity trains in the United States (the Sunset Limited used to run from Orlando to Los Angeles until August 2005 when Hurricane Katrina truncated the route to New Orleans). Any intercity trains out of Penn Station only go as far as Chicago, requiring a change of trains there. Also, although Amtrak has trains to Denver and St. Louis, completely different trains reach these cities from Chicago - the Texas Eagle for St. Louis and the California Zephyr for Denver.
In The Titan's Curse, the heroes board an autorack freight train in Washington DC and wake up the next morning in Cloudcroft, New Mexico. It should be noted that the nearest railroad to Cloudcroft is in Alamogordo. Furthermore, it's impossible to travel the distance overnight, although it's also possible Apollo had something to do with speed up the pace of the journey.
Kid Hero: Just about every single half-blood in this book. Just about.
Killed Off for Real: Everyone that dies in the series. Luke not dying even though Percy thought he did in Titan's Curse doesn't really count because Annabeth told him about thirty seconds later that Luke wasn't dead. The only aversion to this is Tyson. Everyone else thinks that Percy dies, too, but since the story is from his perspective so we know otherwise, it doesn't count.
All the incest in Greek mythology is eventually explained in-series by the idea that the gods have no DNA and therefore cannot inbreed. Demigods at Camp Half-Blood feel free to date any fellow demigod who does not share a divine parent—in other words, two Athena kids (half-siblings) would not go out, but an Athena kid and a Poseidon kid might, regardless of their technical relationship.
The Hollywood Sign is the Underworld entrance for the film of the first book.
Lamarck Was Right: The big three weren't born as rulers of their domains, they divided the world up after defeating their father. In addition, gods apparently don't have DNA. As such the heroes inheriting some of their parent's powers, especially when it comes to children of the Big Three, is an example of this.
Does it count as Lamarck Was Right if it's explicitly a divine legancy instead of being biological?
Let's Get Dangerous: In The Last Olympian, it's calm, quiet Sally Jackson and Paul Blofis. Who thought that two humans, one of whom can't even see through the Mist, could kick so much monster butt?
Mr. Chase gets a moment when he manages to kill a large number of the Titan's army using an antique plane he outfitted with a automatic gun that fires Celestial Bronze bullets. He has one of the highest kill counts in the series.
Libation for the Dead: Nico must offer food and drink to consult spirits. One chapter in Battle of the Labyrinth is even titled "Nico Buys Happy Meals For The Dead." Typically he uses french fries and coke.
Minos, his Treacherous Advisor, complains that it's traditional to use animal blood for necromancy. Nico tells him to shut up.
L Is for Dyslexia: Half-bloods are all dyslexic, since their brains are "hard-wired" to read Ancient Greek instead of English. As a result, reading even regular signage is difficult unless it's in very large font.
Like a Badass out of Hell: In The Last Olympian after Percy gets the Achilles curse in the Underworld, he faces off againgst Hades' army and wins.
It's supposed to be the ultimate prison and it's constantly said that no one, even the greatest heroes could escape. Percy does it when he's twelve.
Nico, being the son of Hades naturally screws this trope to hell.
Living Labyrinth: Daedalus's Labyrinth grows over time. It's grown enough to apparently also develop Roman elements.
Load-Bearing Hero: Percy and Annabeth both pull this one, except they're holding up the sky, technically making them load-bearing heroes for the entire planet.
Artemis (preparing to launch Atlas back under the sky):Get ready!
Percy (holding up the sky): Aaaaaargh - ow…
Locked into Strangeness: Percy and Annabeth get matching gray streaks in their hair after holding up the weight of the sky in The Titan's Curse.
Locked Out of the Loop: Percy, for much of the series. Sally and Paul, too. And of course poor Frederick Chase out there in San Francisco.
Lotus-Eater Machine: The Lotus Hotel & Casino, named after the Trope Namer. Time speeds up significantly. Two weeks in that hotel is 28 years in the real world, and one hour is the equivalent of five days.
Loveable Rogue: Hermes, as in mythology—and by extension, most of his demigod children. Luke is a subversion.
Made of Iron: Luke and Percy. And Achilles and the Nemean Lion.
Magic Compass: In The Demigod Files short story "The Sword of Hades", Percy, Thalia and Nico are given a flower by Persephone that will point the direction the thief who stole the titular sword is in. It loses petals the closer the thief gets to escaping.
The centaur Chiron originally appears as a wheelchair-bound Latin teacher. But early in the series, we learn that his wheelchair is merely a hammerspace device to conceal his horse legs. Although he's Percy's mentor, he doesn't merely serve and glorify Percy—he's plenty capable of his own badassery.
Tyson originally appears to be mentally challenged AND homeless. Turns out he's a Cyclops, so his intelligence is naturally lower than a human's. Like Chiron, he doesn't merely serve the humans in the series, and is a complete badass. He always keeps his Cloud Cuckoo Lander and ditzy tendencies, though.
Played straight when Apollo briefly appears as a homeless man.
Mango Of Discord: Hilariously used by the Stoll brothers to pull a prank off the Aphrodite cabin in the Demigod Files.
Marked to Die: Zoe realized from the beginning who the one meant to die by a parent's hand was.
The Marvelous Deer: In the The Demigod Files short story "The Sword of Hades", Thalia is led to meet Percy and Nico by the Golden Hind, which is, in fact, literally gold.
Meaningful Name: Most of the more minor half-bloods have names which reflect their divine parent. Hephaestus has a kid whose last name is Mason, Apollo has sons whose last names are Yew and Fletcher...
Riordan didn't bother with some of the minor half-bloods, but the worst offender has to be Demeter's daughter. Demeter is the goddess of grain, fertility, and harvesting. Her daughter is Katie Gardner.) Grover, who has a big fixation on nature (he's a satyr, it's his job), has 'grove' in his name, along with his surname, Underwood.
Also, in the case of Silena Beauregard (daughter of Aphrodite) whose surname means beautiful gaze in French.
Don't forget Conner and Travis Stoll. The sons of Hermes, god of thieves. Percy even points this one out, it's so obvious. It might be interesting to point out that Conner and Travis Stoll are real brothers who at one point were in Riordan's class. Charles Beckendorf, albeit with a different appearence, was also a student.
A rather tragic example: "Zoe" means "Life". And her last name is "Nightshade." Nightshade is another name for a family of of poisonous plants. Just how did Zoe die again? Oh yeah, POISON was a part of it!
Also Rachel Elizabeth Dare, in a Steven Ulysses Perhero-ish way. And boy, does Rick Riordan feel proud of that particular idea. Her initals are RED, and she has red hair. Probably coincidence.
People might not necessarily remember Mrs. O'Leary, but they sure remember the lantern her cow kicked over.
Also, to the Air & Space Museum in The Titan's Curse due to a Nemean Lion attack (which will certainly put the Secret Service and FBI on high alert), and a lot of trouble at Alcatraz in the fourth (with Kampe and Briares).
Not to mention damage done in the last book.
More Hero Than Thou: Inverted by The Titan's CursePercy practically pleads for Artemis to let him hold up the sky for her because she could fight better than he could.
It's played with in that scene. Percy had no problem with going head-to-head with Atlas. It wasn't until Ares's curse kicked in and sapped Percy's sword skills that he even tries to take the sky.
A truer example: Bianca's body was never recovered, nor is Michael Yew's.
Then again, it's not like you need to find the bodies when Hades or his son can tell you whether or not they really died.
Nice Job Breaking It, Herod: Kind of. By killing Maria di Angelo in an attempt to kill Nico and Bianca, Zeus just gave Nico a reason to hate and want to destroy the gods, which is what Zeus was trying to prevent. Luckily, Nico didn't act on it. But Hades, in anger at his mistress being killed, cursed the Oracle so she goes all crazy. Luke's mom volunteers to be the Oracle but gets driven mad. Luke feels left alone and resents his parents as a result
Nice to the Waiter: Hestia, in the form of a young girl, says that almost no one (including Percy) ever stops to speak with her. Nico di Angelo is one of the exceptions.
No Eye in Magic: Percy, Grover and Annabeth encounter the actual Medusa from Greek Myth. Percy sees her through a glass gazing ball, so he doesn't get Petrified. In The Film of the Book, he uses an iPod Touch to glimpse ahead before turning corners for the same reason.
Noodle Implements: Grover offers to show the Hunters of Artemis to their cabins in The Titan's Curse. When he shows up again while Percy and Thalia are about to break bad news to Chiron, he shows up again, grinning, with a black eye and red lines that clearly look like a slap mark. It doesn't take much to figure what happened.
Noodle Incident: One of the key events of a year at Camp Half-Blood prior to the series involves a centaur in a prom dress; Annabeth remarks, "Now that was a weird summer."
In The Last Olympian, when Percy arrives at Camp Half-Blood:
"Our beach is on the North Shore of Long Island, and it's enchanted so most people can't even see it. People don't just appear on the beach unless they're demigods, or gods, or really, really lost pizza delivery guys. (It's happened— but that's another story)."
This line from The Sword of Hades
Nico (to Persephone): Family spat? You turned me into a dandelion!
This is sometimes used in an individual book to refer to events that happened in previous ones without giving the details away. For example, from Battle Of The Labyrinth, in a conversation between Percy and his mom;
"I told them you were all right," my mom said, but she sounded like the weight of the sky had just been lifted off her shoulders - and believe me, I know firsthand how that feels.
In The Titan's Curse, it's said that the Hunters didn't have a very cordial encounter the last time they were at Camp Half-Blood. Including the fact that they burned down a few cabins.
No Matter How Much I Beg: In Book 2, Annabeth wants to hear the Sirens, but doesn't want to get killed. She then asks Percy to tie her up and never let her go, so Percy fills his ears with wax so he can't hear the Sirens and her pleas. Unfortunately, she still has her knife, so she eventually escapes. Percy comes after her and manages to grab her before she could drown. Also, he realizes that she can't hear them underwater, so he creates a giant air bubble for them to stay in until the song's over.
Fortunately, Percy is savvy enough to know how to avoid the danger.
Ares does pull one at the end of the first book, but only after already losing the fight from getting stabbed in the heel. He was about to go kill Percy for sure when Kronos evidently changed his mind and he settled for cursing Percy and going somewhere to heal instead, turning into his full divine form to warp somewhere else. But looking at it would have killed Percy.
Fridge Brilliance: This is why you never underestimate Aphrodite. Her daughter could have easily influenced the Ares cabin's love for war and loyalty to their campmates.
It is also implied that by that point Clarisse's stubbornness was the only thing keeping the Ares cabin from entering the war. So her cabin-mates were happy to make any excuse to come to the battlefield. Saying "we fell for the disguise" was as convenient an excuse as any.
Parental Abandonment: Every half-blood is abandoned by their immortal parents and gets occasional visits if they're lucky. Lots of half-bloods never even learn who their divine parent is.
Also averted by the mortal parents like Sally Jackson and later Paul Blofis, and Annabeth's parents.
Not so averted by Luke's mom May. She's there, but she ain't there. Thalia's mortal mom doesn't sound like she would have won any parenting awards either, not even when she was alive.
Pet the Dog: Dionysus, who's quite a grouch and always seems happy to put Percy and his friends down, helps out Grover in The Battle of the Labyrinth, supporting him when he announced that the god Pan was dead. He also showed genuine grief for his son Castor when he died, and helped cure half-blood Chris Rodriguez who had previously gone insane. It's also subtly implied that he's a hell of a lot more pleasant when he's around his wife, who he genuinely loves (despite the standard Greek god one night stands applying).
The Power of Friendship: In The Last Olympian, why the Ares's cabin campers followed Silena; they didn't guess it wasn't Clarisse because they wanted to go fight next to their friends.
Power Trio: Typical for anything Greek, since three is a sacred number. So many examples, but here's just a few:
Obviously, the Big Three: Zeus, Poseidon, and Hades.
Then there's their kids, Thalia, Percy, and Nico (they start off numbering four, but Bianca gets offed fairly quickly and before her parentage is even known).
Thalia, Luke, and Annabeth.
It's a camp rule that any hero who sets out on a quest is allowed to take two and only two companions, specifically because three is a good number. The rule is broken twice, the first time with disastrous consequences.
It was actually broken only once—in The Titan's Curse, the first time more than three people travel on a quest was due to the prophecy, but the prophecy warns that "one shall be lost in the land without rain" (Bianca Di Angelo, killed by a defective Talos statue in southwest Arizona) and "another shall perish by a parent's hand" (Zoe Nightshade). Camp rules don't apply when the Oracle is the one that is doing the talking.
The most obvious one: Percy, Annabeth, and Grover. They're the three main ones for most of the quests and are really close.
Product Placement: A freakish amount in the first book. Burger King! Coca-Cola! Oreos Double Stuf cookies! Even Lunchables! And that just scratches the surface. But it's possible that Riordan didn't want to have to come up with too many fictional brand names because that would be too difficult. Exceptions, however, come in the form of the Monster Donut chain.
It's even Lampshaded. During a war, Percy and another half-blood have an exchange about how they need to sleep but really don't want to. Percy, in narration, explains that demigods' dreams suck, since they're frequently visions and prophecies and other psychic junk which isn't fun at all, and the more tense things are the worse the dreams are. For a while, Percy even had Kronos showing up in his dreams to taunt him (and Kronos is good at it, too.)
Pun: Percy is able to sneak these by people who are more familiar with Greek mythology. A shining example from the fourth book... "Red cattle. The cattle of the sun. They're sacred to Apollo." "Holy cows?" "Exactly. But what are they doing—"
Recycled IN SPACE!: Although it's done well in this case. Many of the plots or subplots are the major arcs of well-known Greek myths. The Sea of Monsters is Jason and the Argonauts and the Odyssey stuck together. Silena's fight against the monster in the final book and Clarisse's subsequent beatdown of the monster that killed her is Patroclus stealing Achilles' armor and Achilles' fight with Hector, complete with dragging the corpse around behind her chariot. Riordan was quite clever in working the myths into his books.
This is Justified in the fifth book, when Prometheus says that patterns repeat themselves in the world.
This also comes up in The Kane Chronicles, where the reason gods want mortal hosts is that they can change those patterns.
The series as a whole could be considered Harry Potter WITH Greek Mythology.
In the first case, it's played straight when Thalia joins The Hunters to avoid turning 16. Thus, meaning that The Great Prophecy can't mean her.
It's played with with Bianca. Who was completely in the running for being The Chosen One, except she decided to join The Hunters long before anyone knew that she was a daughter of Hades.
Refusing Paradise: Percy Jackson refuses the offer to become lieutenant to his father, Poseidon, and gain eternal immortality. He refuses it on the grounds that he's about to enter high school and he doesn't want to lose the possibilities his regular life gives him, but it's heavily implied it's so he can stay with Annabeth.
Remember the New Guy: The Mist can be manipulated to create Fake Memories of a person. For example, after Mrs. Dodds (Percy's teacher and a servant of Hades) attacks Percy and is killed, a new teacher named Mrs. Kerr mysteriously appears to take her place, and nobody but Percy remembers that Mrs. Kerr hadn't always been their teacher.
Rhymes on a Dime: "Curse me, eh, I'll make you pay/ I don't want to rhyme all day!"
Riddling Sphinx: When Percy, Annabeth, Grover and Tyson meet a sphinx in the Labyrinth in Battle of the Labyrinth, it tries to administer a multiple-choice standardized test, with mundane trivia questions (in the style of a game show with regards to her tone of voice, and the use of recorded applause from hidden speakers). Annabeth, who was expecting a riddle that would test her cleverness, is not amused.
Rick Riordan lives in San Antonio, Texas, and wrote the scene as a jab at the TAKS, the standardized test of Texas's grade schools at the time of publishing. The Sphinx's instructions being word for word the script teachers have to recite down to the instructions given on properly bubbling in the answers.
Running Gag: Characters cursing in Ancient Greek, or, "I said something really intelligent like..."
School Saved My Life: Chiron points this out about Percy's Greek History before Percy knows anything. Then it is taken to the extreme when he goes to Camp Half Blood. Played straight for almost everyone.
Science Is Wrong: Among other things, the seasons are caused by Persephone moving between the Underworld and Olympus, not the Earth's tilt, and global warming is simply Zeus being ornery. However, it's implied that there might be a combination of both, as the moon and sun clearly exist as physical forms, not controlled by Apollo and Artemis.
The Scottish Trope: Saying "The Furies" or the names of any god or titan causes thunder to rumble (and apparently, gives power to that god/titan). Even when there aren't any rain clouds around. At least once or twice in book 1, Grover is about to refer to the Furies as such, but changes midway through saying it to say "Kindly Ones".
Self-Fulfilling Prophecy: Zeus killed Maria di Angelo in order to prevent Big Three children so that Kronos won't try to take over the universe. Hades, in anger at his mistress being killed, cursed the Oracle so she goes all crazy. Luke's mom volunteers to be the Oracle but gets driven mad. Luke feels left alone and resents his parents as a result. Kronos uses this as an opportunity to manipulate Luke into helping him rise. Zeus just caused the prophecy to take place in the worst way possible.
That is the beauty of it. You can't fight fate: the only way to not fulfill a prophecy is to simply not hear it, because once you do, it will happen.
Shadow Walker: Nico di Angelo is able to "shadow travel" because he's the son of Hades, he claims that every shadow is one and the same, however he can only do it a couple of times per day preferible at night, also it drains him a lot to the point the first time he used it he passed out for a whole week
Also, Mrs. O'Leary, like all hellhounds, can do this.
Shipper on Deck: Aphrodite is a big Percy/Annabeth shipper. Though (understandably) she thinks life is a soap opera (Lampshaded by her beau, Ares), and so assures Percy that she won't let things be easy for them (unintentionally lampshaded by Annabeth herself at the end), with plenty of Wangst, indecision, etc.
Ship Tease: Thalia/Luke. Two best friends who ran away together for roughly three years. Then Luke joining the Titans because one of his reasons was because of her death.The Titan's Curse also has a lot of moments where you find out that Thalia once considered joining the Hunters, but did not want to because she would be away from Luke. Then there was their final battle in The Titan's Curse which implied quite a bit.
Also, Annabeth/Luke. It started out as a crush on Annabeth's side. Annabeth also defends Luke many, many times in the books. In The Last Olympian, Thalia said that she [Annabeth] always saw Luke as her hero.
And there are so many Percy/Annabeth moments that it could make a shipper faint.
Ship Sinking: Thalia/Luke by the end of The Titan's Curse. Good luck, shippers.
Though fans still ship them. There is the whole breaking her vow thing there. And Thalia seems to generally care for him, still. It did seem like Luke was shunning Thalia by the fifth book when he went to Annabeth's house and said that Thalia would never leave the Hunters. But by The Last Olympian, it implies that Thalia enjoys being part of the Hunters. She's the freakin' lieutenant.
Shout-Out: Too many shout outs to Greek Mythology to list. This is in part because author Rick Riordan is also a Greek researcher.
The Empire State Building's guard with the special 600th floor card for Mount Olympus apparently keeps up with Young Adult Literature fads.
The books also have a character called Will. Will's namesake is a shout out to a certain play write and poet who, in universe, was said to also be a son of Apollo.
Shown Their Work: If a monster is named in the books, it exists in Greek Mythology exactly like it does in the books. References to the Illiad and The Odyssey abound. if there's a place described that exists in real life you can recognize it from descriptions. Even epithets are alluded to (grey eyed Athena for instance). Riordan has clearly read the Theogony, the Illiad, The Odyssey, and a number of other minor books including Ovid's Metamorphoses. It shows up with bits like Apollo mentioning he really hates it when girls get turned into trees, or a thermos that perfectly mimics Odysseus' bag of winds.
Rick Riordan had been an editor of mythology books in the past - and it shows. He even brings other mentions into its sequel series, bringing in "Roman aspects".
Snicket Warning Label: Percy warns you that you should immediately put the book down if any of the descriptions of a demigod sound familiar to you, because if you figure it out, monsters will find you and probably kill you.
Soft Water: Percy lampshades jumping from the St. Louis Arch in the first book, by saying that he is expecting the effect to be like hitting concrete when he strikes the water. But when he hits the water, he's perfectly fine and not injured in any way for a fall from a height that would certainly kill a normal person. Deliberately Justified because Percy is the son of Poseidon, so water cures him (remember earlier in the book that during the Capture the Flag game, Percy gets cut up by the Ares cabin boys, and his cuts heal the moment they contact with water) instead of killing him.
Spell My Name with an S: Canon example. The two first gods of earth and sky are Uranus/Ouranos/Ouranous and Gaia/Gaea.
Stars Are Souls: In one novel, the goddess Artemis's Lancer is killed. She is honored with a whole constellation.
Steven Ulysses Perhero: Several demigod children, including Travis and Connor "Stoll", the sons of Hermes, god of thieves, and Katie "Gardner" and Miranda "Gardiner" both daughters of Demeter, goddess of Agriculture.
Stuffed In The Fridge: Seems to be a recurring theme in Hades's family, what with being the God of the Underworld and all.
Supernormal Bindings: When Artemis is captured in The Titan's Curse, she's briefly shackled before being forced to take Atlas' place holding up the sky.
Super Reflexes: This is given as the reason why many of the demigods end up diagnosed with ADHD, because of their enhanced "Battle Reflexes". There is a similar explanation of dyslexia being the result of having a brain hardwired for ancient Greek; both were written in for the benefit of the authors son, who has both ADHD and dyslexia.
Take That: The Sphinx scene in Battle of the Labyrinth appears to be a Take That to U.S. education when she tries to administer a standardized test to Annabeth:
"Think? How am I supposed to test whether you can think?"
A much more blatant Take That comes from Thalia in The Titan's Curse
"Ugh. Who picked the Jesse McCartney?"
Theme Naming: Sometimes coinciding with with puns. Other examples include Annabeth, daughter of Athena (and whose name contains 'Athena' plus a few extra letters), Clarisse, daughter of Ares (same case). Other examples include Nico de Angelo and, possibly, Ethan Nakamura ("village in the middle," i.e. divided loyalties).
Too Dumb to Live: Nearly everyone at times, but a particularly egregious example is when they enter Hephaestus' junkyard and after explicitly being told not to touch or take anything, everyone does exactly that. Bianca's death was likely only because she drew the short straw offscreen.
It's even worse for Grover. When told not to touch anything in the junkyard, his immediate response is to pick up a golden crown and bite a piece off! Guess his unconscious eating habits got the better of him.
Took a Level in Badass: Nico, in The Titan's Curse after he realizes he is so much more awesome than he thought.
Also Percy, after taking a dive in the river Styx.
Not only is Nicomuch more powerful than he's initially implied to be; he goes from being an annoying little kid to one of the most deadly demigods alive in under a year. He's literally put himself through Training from Hell.
Totally Radical: Lots and lots of it, probably because it is told from the first-person narrative of a young teen, but actually written by a 40-something.
Intentionally used in universe. This is how Percy realizes the true nature of the Lotus Casino, the kid he's playing with uses old slang that is way out of date.
True Sight: Certain characters can see through the Mist. These are special cases, like Sally Jackson and Rachel Elizabeth Dare.
Tsundere: Several characters, the most notable being Annabeth (who is initially mean to Percy - whether this is due to him being a son of Poseidon or the fact they end up hooking up is unknown) and Clarisse (The Stolen Chariot side-story reveals her worst fear to be her father's anger).
Trailers Always Spoil: If you see the cover of the first book, or the movie posters or trailers, and have any amount of Greek Mythology knowledge at all, you'll know that Percy is Poseidon's kid as soon as half-bloods are first mentioned.
Underside Ride: In The Sea of Monsters, Annabeth realizes that the sheep is Percy's way to sneak into Polyphemus's cave to rescue Grover and Clarisse. Promptly, we cut to Percy riding on the underside of Widget, one of Polyphemus's lighter weight sheep, as an invisible Annabeth tells him to hang on.
Unperson: In The Titan's Curse, when it was discovered that Zoë Nightshade betrayed her sisters, the Hesperides, by helping Hercules, they kicked her out and any mentions of her were erased completely. It's implied, though, that she may have actually helped Hercules on all of his other nasty jobs, such as the Hydra and the Nemean Lion.
Unwitting Pawn: The gods,Half-bloods,practically everyone throughout the series has been used at some point
Unusually Uninteresting Sight: After The Titan's Curse, Percy and Annabeth both have matching streaks of grey in their hair from the effort of holding up the sky. This is never mentioned again, and none of the people who show up later notice this.
Many Demigod events that happen in public - you can have a fight with monsters and we will not notice anything. In The Last Olympian, the reason why no one ever thinks Mrs. O'Leary is odd in Manhattan is because either they don't see her, or because Percy speculates that they actually see her as a truck of some kind.
A special mention goes to the "The Sword of Hades." While Percy was taking a test in the auditorium Mrs. O'Leary, a hellhound the size of a hummer, comes bounding in. Everybody else sees a poodle. Percy shocked that the mist
The Laistrygonian fight in the start of The Sea of Monsters. Seriously, the coach must be deaf if he can't see that the new "visitors" are very dangerous.
Weirdness Censor: The Mist, eventually revealed in The Demigod Diaries to be controlled by Hecate.
Weirdness Magnet: Half-bloods have a 'scent' that mythological creatures (mostly monsters) can pick out and follow. If you are not strong and/or are unaware that something's weird about you, the scent is weak, enough to make monsters suspsicious enough to check it out but not enough to be certain. But if you realize you are not normal, that intensifies the scent and can make monsters certain enough to attack; after that, you can basically count on monsters seeking you out in the real world and attacking every now and then. The reason you learn not to use cell phones is because cellular signals send messages to the monsters that say, "Here I am! Please rearrange my face!" At the summer camp/safe haven, most of the camp activities involve combat, fitness, and survival skills for good reason.
The Demigod Diaries expands on this in the short story "The Son of Magic," wherein it's revealed that Lamia cursed all Half-Bloods to be easily detected by monsters, in order to have revenge on Hera for cursing her.
Percy, too. Grover points this out in the first book.
Grover (to Percy) "You're glad your dad is alive. You feel good that he's claimed you, and part of you wants to make him proud. That's why you mailed Medusa's head to Olympus. You wanted him to notice what you'd done."
This is also a major driving force behind Luke's actions.
Why We Can't Have Nice Things: Percy, in the case of Gabe's Chevrolet Camaro, Paul Blofis's Toyota Prius, Meriwether College Prep's gym, the St. Louis Arch, Alcatraz, Mount St. Helens, Goode Middle School's band room...New York City...
What Measure Is a Non-Human?: Percy is much more willing to kill monsters than to kill humans. Justified because monsters come back to life eventually, just not in a very long time, fortunately.
He also can't kill regular people, at least with Riptide. As he learns when cornered by a street gang in Los Angeles.
Wicked Stepmother: Subverted: Annabeth makes her stepmother out to be all sorts of resentful for bringing monsters around, but when we actually meet Mr. and Mrs. Chase in San Francisco...
Smelly Gabe is a male version. Paul Blofis is a male subversion.
Wig, Dress, Accent: Silena Beauregard's Clarisse disguise in the last book. Fooled at least the important people. It is explained that this worked specifically because they wanted to believe it.
Ye Olde Butcherede Englishe: Zoë replaces all of her (second person?) pronouns with this. Thalia gets extremely irritated with Zoe for this:
Thalia Grace: For you. Not thee.
Zoë Nightshade: But you use you for the beginning of a sentence.
Thalia Grace: And the end. Not thou. Not thee. Just you.
Zoë Nightshade:[throwing her hands up in the air] I hate this language! It changes too often!
This is an especially irritating example given that Zoë is using the thee/thou set of pronouns wrong. Though largely discarded now, they are the English familiar pronouns, like the tú set of Spanish pronouns. Arguably Fridge Brilliance, given that Zoë is not a native English speaker.
It also makes sense for her to use the familiar forms; she has little to no respect for heroes, so why would she use a more polite form of address, especially since they can't tell the difference anyway?
World of Ham: It's a story about Classical Greek mythology, told in the style of a Classical Greek tragedy. This is almost a requirement.
It's lampshaded at one point. Annabeth tells the gods how trying to fight a prophecy almost never works (Yeah, Oedipus, ask your dad how that worked out), and the gods, who don't like being told ANYTHING very much, concede the point.
You Know What You Did: Early in The Lightning Thief, Percy's attempts to ask The Furies why they are attacking him are met with this.