Rabble Rouser: Played with during a major Heat Wave. The Jolly Ollie Man tries to charge the kids outrageous prices for ice cream, and Arnold convinces the crowd of kids to make a bunch of noise and give him no peace until he relents and sells ice cream at a reasonable price. Then Helga climbs on top of the truck and starts taking it even further, urging them to flip the ice cream truck over. Arnold then has to turn around and try to calm them down.
Harold tried drinking raw eggs while training for an arm-wrestling match, but they made him want to throw up.
Subverted in another episode when Grandpa is trying to get in shape. He is shown cracking raw eggs into a glass...and then pours them from the glass into a frying pan to cook them.
Recycled Premise: A fair amount of the later episodes are retreads down the paths of older ones - for example "Helga's Parrot" is a mix of "Helga's Locket" and "Helga Blabs It All," all of which are revisitations of the early episode "Little Pink Book." In an example of Tropes Are Not Bad, most of these recycled plots allowed the writers to explore the storylines in unique and still entertaining ways.
The most prominent example, however, is "Love and Cheese," which is "Operation Ruthless," just with Lila replacing Ruth while showing off the deeper development the characters had been given in the years between the episodes. Fully cognizant of this, the episode is full of references to Ruthless - several lines from the first episode are repeated and/or referenced, Ruth herself cameos on several occasions in the background (despite not appearing at all in the show for quite a while), and Phoebe and Gerald are shown walking past scenes together - a reference to how they hooked up in the background during the plot ofRuthless.
A more subtle example is "Arnold Visits Arnie." "Weird Cousin" involves Arnold's cousin Arnie visiting the boarding house and the girl Arnold loves falls in love with Arnie. In "Arnold Visits Arnie" Arnold visits Arnie out in the country and Arnie's girlfriend falls in love with Arnold. It doesn't stick out as much as other examples because there's no subplot where the girl who likes Arnie tries to make the other girl jealous and "Weird Cousin" didn't have Dopplegangers, Arnie aside.
Running Gag: While Helga fawns over Arnold and recites her poetry about him, Brainy will interrupt her with his heavy breathing, resulting in Helga hitting him with an Offhand Backhand. Also, Brainy appears in some of the...weirdest locations. They even lampshade this, and he doesn't even know what he was doing there with them in the first place.
Helga: Look, Brainy, this is just weird. How is it that you're standing behind me again? How'd you get in this little arch? Were you waiting for me to come to this alley? What's your deal?
Every time Arnold hits a baseball, someone is going to get hit by it. There was even an entire episode dealing with the idea.
Harold twice in the episode "Hey Harold", first to his overbearing parents then to Sid and Stinky.
Arnold says this about Lila in her first episode, which complicates things when he realizes he does like her.
Shipper on Deck: Most people who knew about Helga's feelings for Arnold were supportive of a potential relationship, especially Phoebe and Grandpa Phil. Even Lila, her supposed arch-rival, agreed to step aside for her since she actually has no romantic feelings for Arnold.
Sibling Yin-Yang: Helga is constantly ignored and would like some adoration from her parents, while her sister Olga gets all of the attention and would like to be left alone.
Sick Episode: Helga thinks she's sick with Monkeynucleousis and will die soon, but it turns out she's only being paranoid. She's also Completely Missing the Point, as she read about the disease she thinks she has in a book called Diseases Long Since Debunked By Modern Science.
Silly Reason for War: In one episode Grampa takes Arnold and his friends to a reenactment of the Pig War, which in their version of history erupted into all-out war (we know it's not one of Phil's tall tales because of the other people at the reenactment).
Helga's mom is clearly alcoholic, her dad is about as abusive as you can get without being violent, and they're both often pretty neglectful of her. YMMV though - It's shown that they can take care of her, and Miriam was intended to go to Alcoholics Anonymous in The Patakis.
Arnold's in rather good hands; although his grandma is a Cloud Cuckoo Lander and his grandpa has...done some things to Arnold that is child endangerment or negligence, but it's Played for Laughs. In Biosquare, when Helga starts to flood the greenhouse after breaking the sink, Grandpa mistakes their banging for help as a sign to turn the water flow up and make the greenhouse flood faster. In On the Lam, Arnold is clearly tied up and Grandpa just assumes he's playing secret agent.
Played entirely straight with Stoop Kid, a kid who's living by himself with no adults, looks to be well into his teens and apparently hasn't been to school before in his life (After all, Stoop Kid never leaves his stoop) and almost everyone in the neighbourhood knows who he is and he regularly yells at people going past his house. Hasn't anybody thought of calling social services on him?
Left the Background Music On: In "Olga Comes Home", before Helga admits to changing the grade on Olga's report card, she turns off the radio playing Mozart's Requiem which had played every time Olga was seen moping over her B+.
Status Quo Is God: This is a Kid's show, after all, without much semblance of continuity or an overarching plotline. However, there are some implications of some mini-arcs, such as Arnold's relationship with Lila. The Character Development is also an aversion.
Strange Minds Think Alike: This is used a lot. For example, in "Downtown as Fruits", Arnold and Gerald say "Boy, people downtown sure are friendly." when they receive a bag full of cash. They later give the rest to a family stranded with a broken-down car, who then say the same thing.
Arnold: "This doesn't by any chance have anything to do with Helga, does it? Because of the way she treats you?"
Phoebe: (increasingly frazzled) "That's completely ridiculous! Just because Helga's been waiting on me hand and foot ever since the bus accident - that was essentially her fault - doesn't mean that I'd falsely prolong my injury in some kind of passive aggressive attempt to reap the benefits of her guilty conscience and simultaneously give her a taste of her own bossy medicine!"
Superstition Episode: In the episode "Friday the Thirteenth" it's Friday the thirteenth and Arnold's and Gerald's families insist they carry around good luck charms and avoid unlucky things. Arnold and Gerald try to prove superstitions are false, but end up with bad luck. Because Wolfgang gave it to them.
Surrogate Soliloquy: Helga will often whip out her heart-shaped Arnold locket to talk to when she is alone.
Tattered Flag: In the Christmas Episode, Mr. Hyunh is telling Arnold about how he gave up his only daughter during the Vietnam War. During a scene depicting (possibly) the Fall of Saigon, a tattered (American) flag is prominently displayed.
Protesting the shortage of supplies, the teachers went on strike. Because of the strike, the kids rejoiced that they could spend their days out of school, but found that the teachers all had found temporary jobs at all the places they liked to hang out such as the arcade, the bowling alley and the aquarium. The kids return to school to avoid the teachers, but are evicted by Principal Wartz and tells them every day the strike goes on, they cut days from summer vacation. Arnold vows to end the strike as soon as possible.
The Thanksgiving special shows Mr. Simmons having his class put on a play of a very ideal Thanksgiving dinner, which Helga and Arnold lament that they won't have due to their dysfunctional families. They decide to abandon their families and visit Mr. Simmons for a chance at a normal Thanksgiving, only to discover that his family all hates each other.
The Ghost: Lampshaded with Mr. Smith. An episode was dedicated to Arnold and Gerald trying to track him down to deliver a package (apparently they had never seen him either). They were unsuccessful in their attempts.
The Show Must Go On: In "Downtown as Fruits", Helga stalls for time in her play because Arnold and Gerald aren't there when it's their turn to go on.
Throw the Dog a Bone: Arnold tries to invoke this with Eugene in "Eugene's Bike", but even that doesn't stop the poor kid from getting hit with a baseball, choking on a hot dog, and getting seasick. It sort of works in the end, though, since Eugene still thinks it was an awesome day simply because he got to do so many fun things.
In "Helga's Love Potion" Brainy, after countless Offhand Backhand from Helga, is kissed by her (in his forehead). He faints... of happiness!
Token Minority Couple: Some episodes had Gerald, Arnold's Black Best Friend, paired with Phoebe, Helga's half-Japanese best friend. Then again, it could be said that it is a multiracial pairing so it could be something of a subversion. Given the rest of their classmates they were probably better off.
The Ugly Guy's Hot Daughter: Possibly Subverted. Helga and her father both have unibrows, potato noses, and billy goat shaped ears, and Helga is comically mistaken for a boy once. At the same time, the show has an exotic and unusual style of character design, and one need look no further than the Football Head Arnold himself for proof of this. Also, older mature Helga as seen in a few episodes is dropdead gorgeous. In contrast, Olga (Helga's older sister) is obviously perceived as pretty by others in the show.
Unknown Rival: At no point in any episode involving her does Lila ever learn about Helga's animosity for her or Arnold-related jealousy. Ironically, if she did know she would probably have no problem helping Helga—and during the school play and masquerade episodes, does help—since she doesn't have feelings for Arnold anyway, but Helga insists on being antagonistic instead. Word of God is that in "The Patakis" spin-off that never was, Helga finally would have gotten the hint and become friends with Lila. The fact that Arnold would be Put on a Bus probably helped matters between them.
Urban Fantasy: Some episodes fell into this, namely the ones dealing with urban legends like the demon train and ghost bride.
Vanity Is Feminine: Played with when the girls throw a makeover party and deliberately exclude the tomboyish Helga. When Helga tries to play with the boys instead, they mock her for being ugly and unfeminine. Helga caves and dolls herself up, then joins the other girls at the party. After a while, she starts to realize how ridiculous the whole thing is, considering their age. "We're nine years old! We don't have signs of aging!" She persuades the other girls to her side... and they wind up administering the intended makeover to one of the unfortunate boys who tried to crash their party and found himself outmatched.
Helga and Phoebe, though by the end of the show this was shown to be Helga being carelessly demanding rather than actively, intentionally controlling.
A very strong Type 2 in Grandpa Phil and Jimmy Kafka, who are best described as best friends who simultaneously like and hate each other. This is mostly because both of them are prideful, competitive, and incredibly stubborn. As a result, they spent decades not speaking to one another, a fact which both of them are shown to severely regret in the episode where he appears.
Dino Spumoni and Don Reynolds in "Dino Checks Out" and "Partners".
Vocal Evolution: Note, this only applies to characters who retained the same voice actors throughout the entire run of the show.
Helga's voice progressively becomes deeper, and also has a more mature tone to it, which actually works rather well for a character whose had to learn to look out for herself at such an early age.
Stinky's voice takes on more of an exaggeration of a stereotypical southern/hillbilly accent, with a more nasally quality as well. By the final season, his voice has dropped considerably.
Gerald's voice changing becomes a plot point; in reality, Jamil W. Smith's voice had broken, so an episode in which Gerald has his tonsils removed, thus bringing on a change in his voice, was written.
The hammy factor in Harold's voice took a season or two to start shining through, and after that, it gets cranked up more and more, especially when he goes into his crybaby mode.
We're Still Relevant, Dammit: In an in-universe example, Dino Spumoni's backstory shows us that he was trying way too hard to roll with the times, such as creating a rap album in the '80s. He fared better when he went back to singing his '50s tunes.
In "Helga's Show," the comedic imitations Helga performs showcasing her friends' idiosyncrasies cause them to shun her. Taking Phoebe's advice, she tries a kinder approach to her humor, which falls flat. Ironically, it's Arnold who suggests that she go back to the edgier material she used before, which works.
"Big Bob's Crisis" has the head of the Pataki clan take a kinder, simpler, less-stressful approach to life after a gas attack scare (previously thought to be a heart attack). When he begins to give up all of their modern conveniences (and she sees how others start to walk all over him), Helga tells him that she relies on him being the tough, take-charge man she knows he is. After some soul-searching, Bob decides that he can be that man and still take time away to unwind.
Tucker, Coach Wittenberg and Trish's son, is never seen after his first appearance even though his parents show up several times afterwards.
Helga's pet Monitor Lizard only shows up in one episode. It is possible her parents made her get rid of it.
In the episode where Harold worked at Mr. Green's butcher shop; Mr. Green hires Harold as an apprentice at the end of the episode. Ever since we have never seen Harold working at the shop or it being mentioned.
What The Hell Helga: Practically all the kids present in "Helga and the Nanny" called her out for framing Inga for theft.
Worst News Judgment Ever: When Stoop Kid was revealed to be afraid to leave his stoop, the story dominated the front page of the newspaper. His stepping off did, too.
The Worst Seat in the House: Arnold and Gerald once wanted to go to a baseball game to see Arnold's favorite player play his last game before retiring. They decide to buy two tickets from a scalper promising them great seats for half the price of what they're selling at the ticket booth. It turns out that their seats are both in the nosebleed section and obstructed by a pole. Arnold decides to get closer to the action and ends up catching the home run ball from his favorite player at his final at-bat while simultaneously being chased by ushers.
Grandpa once said his grandfather lived 1830-1921. He also said his grandfather participated in the tomato incident which took place in the 1770s-1780s (making him about 150 years older than Phil at least!) and in another episode we see a flashback of Phil's childhood in the mid-late 1920s where his grandfather is shown to be alive and well and only looking about as old as Phil does now.
The writers seem to flip-flop between having Harold a few years older, or the same age as Arnold and his friends.
Yiddish as a Second Language: In "Deconstructing Arnold" Harold calls Arnold a "Kibitzer": Yiddish for a non-participant person, offering (often unwanted) advice or commentary. Or as he defines it: a "big fat buttinski!"
"Yutz" a Yiddish insult meaning "idiot" is also used occasionally by a few characters. Mostly by Helga.
You Have 48 Hours: the episode "24 Hours to Live". After Arnold accidentally hits Harold in the face with a baseball, Helga persuades Harold to wait until the next day to fight him. And just to really rub it in, Helga spends most of that day counting down exactly how many hours, minutes, and seconds Arnold has to live with a bullhorn.
You Look Familiar: When the original voice of Arnold, Toran Caudell, started getting older, they switched him to the voice of Wolfgang while Phillip Van Dyke took over the voice of Arnold. Later on, Spencer Klein would replace Phillip. This all ended up being subtly referenced in the episode "New Bully on the Block", where Wolfgang, Ludwig (voiced by Phillip). and Arnold get in a war over who should own the vacant lot.
Your Television Hates You: In "Arnold's Hat," Arnold is depressed because he lost his hat. To take his mind off how he feels, he turns on the TV only to discover that it's Hat Day at the local ballpark and everyone is wearing one. It doesn't help.
Your Tomcat Is Pregnant: In the subway episode, it turns out that "Killer", a seeing eye dog, was pregnant and has puppies in the stalled subway car.