When Miles' journal appears at the very beginning of the movie (when it spins into view, and in Arnold's dream), several of the pages are readable entries previously read in "The Journal". One of the last pages says at the bottom: "We're going to have a baby!! I hope he's a boy, so we can name him Arnold, and he can have his own series, make 100 eps,"
The inside of the temple in Arnold's dream is a ruined version the boarding house hallway (the stairs that lead to Arnold's room and the W.C. door are visible). There are statues of Phil and Gertie next to the "front door" of Sunset Arms. The stairway the obscured Miles and Stella are standing in is a bigger version of the stoop, and the outside area is a jungle version of the neighborhood.
When Lasombra's laptop detects Arnold's football head, the outlines of a fire hydrant, the state of Texas, a pineapple, an apple, a tea pot, a chicken and a football appear.
This film officially reveals Arnold's last name; "Shortman".
Two of Lasombra's mooks are in the parade crowd.
The pirate with the blue shirt and the red and white cap seems to be named "Paco", which is a nickname for "Francisco".
As of the end of the movie, the bald spot on Arnold's head left by his hat is gone.
The movie's closing shot, of Miles and Stella in P.S. 118's stoop, mirrors the shot of the obscured Miles and Stella on the "stoop" in Arnold's dream at the start of the film.
The movie includes dedications in loving memory of: Steve Viksten, original writer and voice of Oskar, who passed away at the age of 53 due to a heart attack on June 23, 2014; Vincent Schiavelli, original voice of Pigeon Man, who passed away at the age of 57 due to lung cancer on December 26, 2005; and Kevin Iwaki, the film's archives coordinator, who passed away at the age of 30 due to acute leukemia on January 13, 2017.
Also included is a Thank You to "all fans who wrote letters and signed petitions encouraging the making of this movie".
Deleted Scenes: A lot of the movie's original script was taken out for time. However, Craig said in Anndi McAfee's post-premiere live chat that most of the deleted scenes were cut before the animation phase.
As seen on a NickSplat "Behind the Scenes" clip, one scene that was originally longer in the storyboards was the parade scene, with Olga appearing on one of the parade floats, and Helga dressed as a monkey. Other scenes storyboarded but not animated can be seen here.
In an interview, Craig Bartlett mentioned a cut scene in the temple Arnold was born in ("The Journal") featuring a reunion of the characters, including Helga and her parents reconciliating.
Some finished animation was also cut for time. A shot of Arnold, Helga, Gerald, and Phoebe on the boat (posted by Craig Bartlett on his Instagram) and another shot of the airport's departure screen (shown in NYCC 2017) are not in the aired cut of the movie.
A background character called "Hipster Toran" was designed, but does not appear in the actual movie.
In one of the trailers, Mr. Hyunh said "A pig eating bacon? That is not okay!" This line was changed for the actual film.
This is the second Nickelodeon revival movie and the first one to be based off a Nicktoon.
This film is rated TV-PG, unlike the TV series, which was rated TV-Y (TV-Y7 for later reruns). The movie's rating comes from the on-screen violence and character deaths.
Compared to the original series, this movie has thinner character outlines, more vibrant colors, cleaner animation, and brighter backgrounds.
Like Hey Arnold! The Movie, this film uses 3D models; the journal at the start, every moving vehicle, the Corazón, and the Green-Eyed People's city.
To celebrate the film's premiere, NickSplat started airing episodes of the show every week, and began a Hey Arnold! marathon on November 17. The film aired simultaneously on the main Nickelodeon channel, the Nicktoons Network, and TeenNick at 7PM EST.
This is the only time Arnold cries on-screen, not counting the flashback in "Parents Day".
This marks the second time Arnold addresses Oskar by his first name (the first time was in "Hookey"), having before only addressing him as "Mr. Kokoshka".
Craig Bartlett added Pigeon Man in the movie to completely debunk the fake rumors claiming he committed suicide.
Pigeon Man being in Paris is also meant to be a reference to the beginning of the comic story "Gerald's Urban Legends", where Gerald explained what happened to him.
Design Changes: Helga and Big Bob's ears are now smaller, and look more similar to everyone else's ears. Helga's bow is in a slightly different position, and her hair is a lighter color than Olga's. Miles and Phil's chins were redesigned to look slightly less phallic.
Also, the kid characters are drawn with large heads and small bodies. These body proportions resemble the character designs from Seasons 2 and 3, rather than the ones from Season 4 onward.
As a result of their voice actors being changed, Gerald and Stinky sound noticeably more youthful (like their Season 1-2 selves) in this movie than they did in the later seasons of the series. Mr. Hyunh also sounds different, as Wally Wingert is not natively Vietnamese like Baoan Coleman.
Rick Corso almost didn't reprise his role as Dino Spumoni, as he had not done voice acting since Hey Arnold!, instead doing stand-up comedy on cruise ships. Dom Irrera ran into Rick by chance and told him the production team was looking to contact him for the movie.
The shot of Arnold ducking an airplane in the prologue is a reference to the Hitchock film North by Northwest.
Gerald can be seen reading Heart of Darkness when he's walking outside the boarding house.
There are businesses in the background named after Stu Livingston and Raymie Muzquiz, the two directors of this movie.
The mention of Frida Kahlo might be intentional, as Alfred Molina played Diego Rivera in Frida.
When Curly jumps on top of Olga, he shouts, "Hi-ho, Silver!", a common misquote from popular radio character The Lone Ranger. (He actually says, "Hi-yo, Silver!")
During the montage showing how Abner got back to Hillwood, a cartoon version of Craig Bartlett is sitting next to him in first class. He could also be seen in the background in some earlier shots of the city of Puerto Clara.
Eugene rolls down a guard, saying he's like "the big ball from that movie", referring to Raiders of the Lost Ark, which, most likely not coincidentally, featured Alfred Molina in his film debut.
The island from the opening of "Parents Day" appears at the start of the movie. Arnold's pilot outfit and his and Eduardo's planes are both also a reference to the plane and outfits Miles and Stella used when they took off in that episode's flashback.
Many elements and plot points from "The Journal" play a major role in the story. There are also some smaller nods to that episode:
The scene of the mother and father with their child next to the slide calls back to the flashback of Arnold, Miles and Stella in that same park.
In both "The Journal" and the test animation for the original movie, Lasombra wore a black cloak over his upper body, along with a red cloth and a yellow skull mask over his face. The photo of Lasombra in the newspaper of Arnold's room shows him with the same cloak and mask. The mask and red cloth can also be seen hanged inside Lasombra's hut after Arnold escapes. (See here)
The stone shrine Arnold, Gerald, and Helga reach when the amulet stops glowing is the exact same shrine Miles and Stella found when they returned the Corazón over ten years before. (Confirmed by Stu Livingston here.)
It's also revealed that there's an underground chamber beneath the shrine, which (according to one of the mural paintings in the hidden city) is how the Green-Eyes retrieved the treasure so quickly while Miles and Stella had their backs turned.
After she runs into Arnold and Abner near the start of the movie, Helga says she's tried to tell Arnold her feelings, but hasn't received a response.
Helga, on the crow's nest, tells Arnold: "Oh, don't play dumb, Arnold! You know what I'm talking about!" (referring to her feelings for him, and the fact that he already knows about them).
At the end of the movie, Arnold tells Helga: "I know you tried to tell me before, and I wasn't ready to hear it." This line is referring to the confession in the previous movie; not to the near-confession earlier in this movie, as after that line, Arnold says: "But now, this whole thing: the trip to San Lorenzo..."
The scene where Arnold makes way for Helga to cross the street is a reference to the show's opening animation.
Interestingly, the clips from "Harold's Kitty", "Downtown as Fruits", and "24 Hours to Live" seem to be recorded from Helga's P.O.V., as if she had a camera with her while she was there. (All other clips are clearly filmed by Helga while hiding.)
Harold mentions he was a one-dimensional bully before Arnold showed him his sensitive side. This lampshades how in earlier episodes like "Pigeon Man" and "24 Hours to Live", Harold was the main bully role of the show, before he befriended Arnold and Wolfgang took over that role.
Stinky and Harold moon the camera, referencing "Full Moon".
The newswoman that reports the news of Arnold winning the trip to San Lorenzo also reported the news of Dino's supposed death in "Dino Checks Out". The bar on the bottom of the screen also says the same.
Olga being a student-teacher (from "Student Teacher") is the reason she goes on the trip.
Sid's Beatle boots from the episode "Monkeyman!" are destroyed while walking through the jungle.
Curly frees the animals in the pirate hideout and yells "Free the animals in the zoo!", referencing "Cool Party".
When Arnold is opening the Corazón, it's shown that he does indeed have green eyes, as stated by Helga in "The Little Pink Book".
The one-year time skip between the original series and this movie is reflected in a few ways:
Characters: The students are now around 10 or 11 years old, and have started going through puberty. Arnold is slightly taller (his plaid shirt no longer looks like a skirt), Gerald is growing to resemble Jamie O more closely (besides his haircut, the shape of his head also looks more like his brother's), and Brainy and Wolfgang have facial hair. In the case of the girls (most noticeably Patty, Helga and Rhonda), they're developing breasts. And some of the adults have also changed, such as Big Bob having a bald spot, and Mr. Green having grey hair.
Setting: According to Bartlett, after the first movie's events, the neighborhood got discovered by hipsters, and new businesses have been opened in old buildings that were sold to Scheck. P.S. 118 seems to have gotten an expansion and become an elementary/middle school hybird, as a new part of the building can be seen next to the Auditorium, and on the first day of school, Patty (an 8th grader as of the end of the movie) is seen entering the building along with Arnold and his friends. Also, the area under the boarding house's fire escape now has trees.
Technology: Although this movie takes place about a year after the end of the original series, within that year, technology seems to have advanced several years compared to real-world standards: Wi-Fi is mentioned, and flat-screen monitors and iPhone-like cellphones are visible (most notably Rhonda's, though Arnold and a background character also are shown to have one). Canonically, this movie likely takes place in 2002, if you assume "The Journal" took place in 2001, the year it was produced. In real life, all this technology became mainstream in the mid-2000s, with the 1st generation of iPhones coming out in 2007.
The difference between old and new technology is visible in the video footage: The old Arnold clips (reanimated scenes of past episodes, recorded by Helga the previous year) were all recorded on videotape, as they have lower picture quality, rainbow and ghosting effects, and interlaced scanlines. Meanwhile, the newer footage in the video presentation (recorded earlier that day) looks much cleaner and higher quality, and has progressive scanlines and some grain, indicating is was likely recorded on 35mm film.
The camcorder Gerald was using to film Arnold at the riverbank was not the one he used to record everyone thanking Arnold, as it produced video of the same quality as Helga's old recordings, meaning it was an older model. It seems that between the original series and this movie, Helga got a more modern videocamera, which she lent to Gerald so he could record the footage of everyone thanking Arnold (and she could avoid doing so herself, to keep her affections for Arnold a secret). This is supported by the fact that the clip of Arnold finishing the habitat and Monkeyman thanking him is the same quality as the clips of everyone thanking Arnold, and Helga was shown to be hiding there at the time.
The aforementioned technological upgrade has caused Big Bob's Beepers to go through hard times, as beepers have now been phased out in favor of cellphones and Bob refuses to adapt with the times (not to mention a beeper is still $99.99, as seen in the magazine on Miriam's face). The store is seen having a clearance sale, and it's implied (by their mailbox and cars being outside the store, there being a living room of sorts inside, and Bob getting the morning paper at the store's entrance) that the Patakis' house has been repossesed/sold due to financial struggles, and they live in the store now.
Gerald appears to have learned about Helga's secret love for Arnold at some point before the events of the movie. Although it is never explained on-screen how he figured it out, it is implied that either Arnold or Phoebe - or perhaps even both - may have told him:
After Helga snaps at Arnold for bumping into her, Gerald says "Got one more, Helga?" while he (as well as Arnold) has a knowing look on his face.
Gerald shares knowing smiles and snickers with Phoebe while Helga stumbles over an explanation for why she wants to help Arnold go to San Lorenzo.
Helga's botched confession scene obviously mirrors her original confession from Hey Arnold! The Movie: they both take place in a tall, isolated place (the top of the FTi building, and the Doña Marina's crow's nest, respectively), and Helga corners Arnold in both.
Arnold fell for Lasombra's relatively paper-thin impersonation of Eduardo because, not only does the river pirate bear a physical and facial resemblance to Eduardo, but Arnold had no clear visual reference as to how Eduardo actually looked - he only had one old picture of his parents where Eduardo appears blurred in the background. Lasombra also had torn out Eduardo's face from the photo in his apartment, preventing Arnold or anyone else from figuring out the trick. Not to mention that Arnold didn't know how Lasombra himself looked either, as in the newspaper article in Arnold's room, Lasombra is wearing his skull mask.
Stinky finds a green (non-exotic) parrot while walking through the jungle, which can then be seen during several scenes at the pirate habitat. It also appears at the end of the movie, flying out of the boarding house along with other San Lorenzo creatures. Later, when everyone is entering P.S. 118, Stinky asks "Hey, y'all see my parrot?", meaning he kept the parrot as a pet, and he couldn't find it that day as it went into the boarding house.
Lasombra refusing to give Rhonda his Wi-Fi password is a moment that's played for comedy, but actually has a logical reasoning behind it: if Lasombra gave Rhonda the password, she could easily ask for help using the Internet connection.
While the sleeping sickness was described in "Parents Day" and "The Journal" as deadly, it is revealed in this movie that those who contract it (both humans and butterflies) do not outright die, but go into a permanent comatose state until a cure is administered to them, at which point they wake up shortly after.
It's very likely that the Green-Eyes misinterpreted the comatose state as death (like Arnold did when he first saw his sleeping parents), as their mural paintings depict skulls and bones above the infected, despite the disease proving not fatal.
This might also explain why Miles, Stella, and Eduardo believed the disease to be fatal in "The Journal". The trio never saw an affected Green-Eye, they were only told by the Green-Eyes that many had "perished". It's also likely that the affected butterflies found by Stella at the stone shrine were comatose too, but were erroneously labeled as "dead".
Arnold being the one to open the Corazón, a literal heart made of gold, symbolizes his good, pure nature. The treasure not shooting a dart at Helga might be interpreted as it detecting that Helga has a pure heart as well.
At the end of the dream sequence at the start of the film, a heart-shaped hole appears on Arnold's chest, representing the hole left in his heart by the absence of his parents. This hole on his chest is the same shape as Helga's gold-plated heart locket, which itself is a symbol of both her deep love for Arnold, and her hidden pure heart. Symbolically speaking, Helga's locket (and therefore, her love for him) is what filled the hole in Arnold's heart, as it's what activated the medicine machine and reawakened Arnold's parents.
Near the end of the movie, Arnold tells Helga: "I always wondered if maybe you were mean to me because... well, you loved me." This line implies that even before the confession in Hey Arnold! The Movie, Arnold had thought of the possibility that Helga secretly had feelings for him. This possibility was verbally suggested to Arnold by Phil in "Girl Trouble", and in Arnold’s dream Helga confessed in "Married" is strong evidence that, deep down, Arnold did suspect Helga liked him and was mean to cover it up, despite not knowing/believing it was true until her confession.
This movie was focusing on Arnold and Helga.
Helga was eventually redeemed herself to become Arnold's girlfriend.