The episode "Hey Harold!", featuring quite possibly one of the most touching and adorable pairings in the history of animation, Harold and Patty.
Any episode starring Big Patty, really; how Arnold manages to convince her to fake a beatdown on Helga and they share a bit of heart to heart, how Harold stands up to Stinky and Sid when they mock Patty (twice; first time after a dance together, second time after losing an arm-wrestling match to her with pride and dignity) and even Rhonda who gave another snobby materialistic girl a verbal beatdown before things escalated into a repeat of the reform school they both went to, or worse. By the end of each episode, they all gain a bit of respect towards Patty and find that she isn't so bad as they first thought after all.
When Mr Hyunh finally reunites with his daughter in "Arnold's Christmas"
How about Helga sacrificing her own gift (the Nancy Spumoni signature boots that were considered a hot Christmas item) in order to make it happen without any recognition and without any sort of notice. And keep in mind that this was from her parents who seem to have a "Well Done, Son" Guy relationship with her. So for her to sacrifice that rare bit of recognition and love from them in order for Arnold to make Mr. Hyunh's wish come true is just...it's a mix of a Crowning Moment of Heartwarming and a Tear Jerker. And no one will ever know.
Thing is, it almost didn't happen because the guy who wanted the Snow Boots in the first place was just leaving work. Helga doesn't have any of that and convinces him to go back inside to look for Mai, because she knows that Arnold's world view is at stake of being crushed.
Helga: But if you leave now, that little football headed kid will never believe in miracles again.
And making all this even better? Helga had spent the earlier part of the episode trying to find a gift for Arnold that will "make him pine for me the way I pine for him!" It made it even more powerful when she did all this completely unknown to anyone except for the guy she convinced to keep looking.
The end of "The List," where Grandma finally finds a place for her piano, on the roof, after spending all day trying to get in in the house, and sings a song to Arnold, who's had a long string of bad luck, about not letting the misfortunes of life get you down.
The end of "Sally's Comet," when their plan to work get everyone to turn out their lights works so they can see the comet in all its glory, just like Phil did with his dad seventy years ago.
Grandpa Phil/(Flashback)Phil's Dad: "Twenty Three Skidoo! Boys, you're going to remember this for the rest of your lives!"
Arnold: "So, what do you think we'll be doing in seventy years?"
Gerald: "Lookin' at this comet again!"
Phil: "Yes sir! Course, I won't be. I'll be... y'know."
The end of "The Beeper Queen". Miriam's finally taken some initiative and has proven she's more than a "smoothie"-guzzling scatterbrain by taking over for Bob at the beeper emporium, and she loves it. But once she realizes she's neglected Helga, she gives it all up to come back home, and she and Helga even hug. This being the Pataki family makes it all that more meaningful.
Also, any time Big Bob shows some Hidden Depths and love toward Helga.
The ending of "Crabby Author". "Even if you're afraid to go looking for magic, magic still may come looking for you. The end."
The Veteran's Day episode that ended with Gerald's dad re-meeting the man (and meeting the family of) whose life he saved in Vietnam.
Also the ending to "Phoebe Skips". It shows how Helga and Phoebe`s friendship means to each other.
Helga: "You're more than just my sidekick. You're my best friend."
In "Helga on the Couch," the Flashback to how Helga and Arnold first met surely qualifies.
And is preceded by a Crowning Moment of Heartbreaking in the previous scene, where Helga is announcing that she's going to preschool, only to be completely ignored by her parents.
Dr. Bliss' entire character is extremely heartwarming - she's the kind of person a troubled person like Helga really needs in her life, a genuinely good person who became a child psychologist because she wants to help kids. Having barely seen Helga for barely a day, she cares more about Helga than people who have known her for her entire life, and gets her to open up not necessarily by wheedling her but by encouraging her to be better. It's telling that when Helga first walks into her session, she's bitter and combative, but then by the end she doesn't want to go, promises to come back for another session and even runs back to give the doc a big hug.
It's a small moment, but the first time we see Helga start to bond with Dr. Bliss is when Helga discovers they both know the same jump rope rhymes. Cut to the two of them jumping rope side by side while saying the same rhyme.
"Field Trip", where Arnold and his grandma team up to free an old, ill-treated turtle from the aquarium. The episode ends with them watching him swim away to the sea, as the sun rises.
And it sticks, too, flying right in the face of Status Quo Is God. He's now addicted to radishes. ...Well, at least they're healthy.
Arnold hugging Helga at the end of "Arnold Visits Arnie".
Four words: "You keep the money."
This troper hasn't seen the episode in years, but one moment rings in memory: Helga's father gets tickets for a function she wanted to go to, thinking it was a musical. In reality, it was a wrestling match. Despite the mixup Helga and her dad enjoy the show together.
In the Thanksgiving Episode, Helga returns home - expecting her family not to have missed her. Instead, she sees Miriam demanding the police find her missing daughter, Big Bob about to get in his Hummer to patrol the city and Olga having just finished dozens of fliers she intends to hang up. Naturally, they're overjoyed to see her safe and sound, and all admit out loud that they love her.
Meanwhile, at the boarding house, Arnold returns home to gladly celebrate their tradition of Fourth of July (as Pookie flips the holidays every year). However, his grandparents and the borders have set-up a bonafide Thanksgiving dinner for him on the roof.
In "Best Man," Coach Wittenburg asks Arnold to be just that at his wedding - saying he's his only true friend.
Also, him sacrificing the win for his wife - again.
There was an episode where the kids try to take the subway but it ends up malfunctioning leaving them along with a homeless man (Mark Hamill) who keeps telling them to "Get out of [his] house," a blind man (voiced by Kevin Michael Richardson) with his dog, a psychologist (Tony Jay) and his patient (Kath Soucie) trying to overcome claustrophobia, a retired nurse, and an old man stuck underground. Of course tensions run high but near the end, Arnold notices there's something wrong with the blind man's dog and points it out. The retired nurse joins Arnold while the blind man sits back and worries. Some moments later he asks if his dog is all right, Arnold reassures him and tells him his dog was actually female and just gave birth to a litter of puppies. The blind man just starts crying tears of happiness and says "I'm a daddy?!" And to make it even better, the subway turns back on (thanks to Grandma) and everyone cheers!
Note that the subway starts up while everyone was singing a song initiated by the homeless man.
In "Casa Paradiso", where Grandpa tries to sell the boarding house and tries to make Arnold, who refuses to leave, come with him to live in a condo. The heartwarming part comes in as the residents stand by Arnold's protesting of selling their home, and they swear that they'll take care of him.
Arnold singing to an ill Glueboy the mule in "The Racing Mule".
Helga admitting her feelings for Arnold to Lila in "School Play", and Lila stepping down from the Juliet role to give Helga the chance to kiss Arnold, saying she finds her feelings "ever so sweet".
"Phoebe Breaks A Leg" is a true friendship episode for Helga and Phoebe. After Phoebe gets hit by a bus running errands for Helga, Helga is immediately, deeply contrite and vows to be a better friend to Phoebe. She cleans Phoebe's locker, brings her stuff to wash her hair, gets her lunch for her, etc. Phoebe begins taking advantage of Helga after Helga was treating her like staff, but then when Arnold gives her a subtle What the Hell, Hero? and Helga almost gets hit by a bus, Phoebe pushes her out of the way. The two then honestly talk about their feelings when Phoebe visits Helga in hospital. It goes to show that, inconsiderate she may be, Helga truly does have a Hidden Heart of Gold and Phoebe knows this, which is why she's such a loyal friend. Aw.
When Arnold tries to collect money to buy a ticket for Mickey Kaline's last baseball match, Grandpa reminds him about the money earned when Arnold took care of dogs. When he goes to take it out, Grandpa sneaks a bill from his own pocket into Arnold's money.
Provided, he had to retract a bit when it turned out he gave Arnold a $50 bill...
Grandpa driving Arnold to the stadium to give the baseball back to Micky Kaline was heartwarming on its own. To make it even more heartwarming, Micky Kaline decides to play catch with Arnold for a while.
A very subtle moment in the beginning of "Helga's Love Potion" has Mr. Simmons handing back the students' creative writing assignments and quietly remarking to Helga how much he's truly enjoyed getting to know her through her work. It just goes to show what an excellent, devoted teacher he really is.
In "Olga Gets Engaged", Helga was perfectly willing to let Olga throw her life away so she can marry to her fiancÚ, Doug, who was really a smooth-talking con-artist. Helga soon realizes she can't go through with it and threatens Doug to leave before she reveals his true nature to everyone. He asks why she would do this despite her resent towards Olga, and her response? "When your sister's in trouble, you're supposed to do something about it. It doesn't matter if you like her or not, you're supposed to do something."
What prevents "Pigeon Man" from being a complete Downer Ending is that Pigeon Man now knows that there are good people like Arnold and hopes to find someone like him.
"I just hope there's another Arnold where I go next..." *sniff*