In the episode "Road Trip", Helga turns on the car radio to a Hard Rock music station, suggesting that she enjoys music within the Rock genre.
In "School Play", Helga's mother, Miriam, yells into her bedroom and asks her if she remembered to take her constipation medicine in which Helga responds with a yes.
According to Sheena in "Phoebe Skips", Helga has a gastrointestinal disorder.
In "Student Teacher", Olga tells Mr. Simmons' students a story about a little girl who was a bedwetter overcame her problem. It is at the end of the story that Olga reveals to the students that the story was about Helga, who was a bedwetter until the age of 7.
In the Angry Beavers episode "Dumbwaiters", the beavers showed a Helga Pataki mask within a set of scary masks.
Several episode plots revolve around Helga trying to recover something that outwardly states her feelings to Arnold, and ended up in Arnold's hands.
Youtuber Bo Burnham mentions Helga Pataki in the line "Hatin' other rappers like I'm Helga Pataki" of his song "Words, Words, Words".
The names Helga gave her fists, "Ol' Betsy" and "The Five Avengers", don't make much sense because everyone has three fingers and one thumb.
Though Helga's huge crush on Arnold was initially a secret, over time, more characters learned about it.
Brainy: He knows about her secret because he's stalked her for years and hears her soliloquies.
Big Patty: She figures out the truth on her own in "Helga vs. Big Patty"; she asks Helga if she and Arnold "have a thing for each other", and the two smile knowingly.
Phil and Gertie: In "Girl Trouble", Phil speculates (from personal experience) that the reason Helga picks on Arnold is because she has a crush on him, and mentions he always sees her outside Sunset Arms waiting for him. In "Helga Blabs It All", Gertie heard Helga's complete voice message confession, though she did not properly relay it to Arnold. Also, the two saw Helga in the boarding house at least twice ("Helga's Parrot" and "Helga Sleepwalks"), while Arnold did not.
Lila: Helga admits her secret to her in "School Play", and Lila mentions she already "had a funny feeling" Helga liked him.
Arnold: Needless to say, Arnold conclusively found out Helga's feelings for him in Hey Arnold! The Movie, even if he wasn't ready to hear the revelation at the time. Before he found out Helga has a crush on him, Arnold had wondered about the possibility (Hey Arnold! The Jungle Movie) and subconsciously knew it to be true ("Married").
Gerald: By Hey Arnold! The Jungle Movie, Gerald seems to already be aware of Helga's secret, as he grins knowingly with Phoebe while Helga stumbles trying to make an excuse for helping Arnold go to San Lorenzo.
Also, the other kids entered Helga's Arnold-tape-filled basement. It's possible they might know as well.
Helga said in the episode "Arnold's Valentine" that she likes a man who's honest "love-wise", possibly because she doesn't want to end up with a dysfunctional marriage like Bob and Miriam.
Even though she wants a family who would pay attention to her, when they do she mostly tends to brush it off or isolate herself by saying that they're either embarrassing her or making her miserable.
Though Helga is mostly a tomboy, she has been shown to be feminine at times.
Helga may be mean, but whenever the situation is right, she can be characterized as caring, deep, and serious towards the people she's close to like Phoebe, Arnold, Olga (once in a while) and her parents (to some extent).
In the episode "April Fool's Day", Arnold mentioned (when giving a gag present to Helga) that Helga's birthday was "last week," which means that her birthday falls on a day between March 19 and March 31 (which makes her an Aries). Among fans, Helga's birthday is most often considered to be on March 26th, Francesca Smith's birthday. This also means Helga turned 10 in "April Fool's Day".
Helga seems to be a fan of Nancy Spumoni clothing and other items. Nancy Spumoni is a loose parody of Roxy clothing.
A Disney character, Isabella Garcia-Shapiro from Phineas and Ferb, has a similar outfit to Helga Pataki's. Also Dan Povenmire who worked on Hey Arnold! is one of the creators of Phineas and Ferb creating another connection.
Grandpa sometimes calls her Arnold's "ugly friend with the one eyebrow" (in reference to her monobrow).
Helga appears to like the color pink, because throughout the show, almost all of her outfits are pink. This contradicts with her image as a tomboy because pink is usually considered a girlish color. This could be because when Helga first met Arnold, he complimented her bow saying it was pink like her pants and she most likely adopted the color pink as her favorite because of this.