Adorkable: Tod. Whenever he's around Vixey, he gets all goofy and tongue-tied.
Angst? What Angst?: Tweed drops Tod off in the forest minutes before a rainstorm, leading to the most miserable night of his life. The next morning, he gets one look at Vixey and forgets all about those pesky abandonment issues. Even when we see him forlornly looking down from a hill at the end of the movie, it's framed more as him missing Copper than the woman who raised him.
Applicability: Two innocent young kids become friends because they're oblivious to how the rest of the world sees them, and then grow up into the roles society expects of them and are torn apart. There's also these lines from the song "Best of Friends":
Broken Base: Disney fans are split between whether this is a heart-wrenching childhood classic or the red flag of Disney's Dork Age finally hitting an all-time low.
Ensemble Darkhorse: The bear only appears for a brief scene at the end of the movie, but his appearance is considered one its highlights.
Harsher in Hindsight: In-narrative, considering the traditional mating patterns of foxes, since only Tod's mother is seen taking him to safety, it's likely that the rest of his siblings (foxes never have just one cub at a time) had already been killed, and his father likely stayed back to try and protect them from the hunters. When Tod takes a stand to try and protect Vixey, he may be unknowingly following his father's example.
Hilarious in Hindsight: Kurt Russell recorded his work for this film at the same time he was playing Elvis Presley in a TV biopic, where he performed "You Ain't Nothing But a Hound Dog."
Ho Yay: Todd and Copper's friendship could be seen as this. Interestingly, this fits further with the above mentioned Applicability—just imagine if this story was about two human boys. Satellite Love Interest Vixey appears to have only been put in the movie to avoid accusations of this.
Just Here for Godzilla: There are actually some people who only watch the film for the Dinky and Boomer scenes.
Moral Event Horizon: Amos Slade comes dangerously close to crossing it when he attempts to shoot Tod after he saved their lives, but manages to avoid it and even performs a HeelFace Turn when Copper convinces him that he's not their enemy.
Shipping: Given the fact that their relationship drives the plot, it's not surprising that Tod and Copper get their share of this. Even better, it takes the above mentioned Applicability to a whole new level...
Widow Tweed and Amos Slade also count, hilariously enough. Tweed fussing over Slade's injuries at the end and bandaging him despite his protests looks almost Slap-Slap-Kiss.
Tastes Like Diabetes: A common misconception of the film due to how it's advertised. While there are a few overly cute scenes during the eponymous duo's childhood, the movie is actually taken very seriously and is much more adult-appealing than most people seem to realise. Played more straight for the Denser and Wackier Interquel.
Many fans think Chief should have been Killed Off for Real to make Copper and Amos Slade's anger more justified and overall have made the latter half of the movie a lot darker. It turns out that the writers were going to kill Chief off (as in the novel) but decided against it because they thought it'd be too dark. Chief's original fate is apparent when Copper finds him after he's jumped off the bridge: a dog lying motionless with his nose in the water is pretty much dead. But Disney decided to draw the line there.
When Copper returns from his hunting trip with Amos and Chief, some fox pelts can clearly be seen on the pile of fur he's helped collect. You'd think it'd be an interesting/important moment to show the first time he had to chase a fox and/or watch Amos shoot it, but we never see it.
The movie as a whole is this for some. While it's obvious the film really wants to dip in the dramatic parts and be seen as a serious film, it can't commit itself fully to presenting itself that way due to having to stick to "Disney elements" like the out-of-place comic relief or the shallow love story.
The novel: Some find that the title characters are too unlikeable to feel too bad about their world being destroyed.
The film: A case that can be blamed entirely on Executive Meddling. As noted above, Chief was originally going to be killed by his fall from the train tracks, and by having him live but not changing anything else, Copper comes off as unbelievably petty for wanting to murder his childhood friend and his mate over an accident that had no permanent consequences.
Values Dissonance: Amos Slade's comments to Widow Tweed after she takes away his gun and at the end of the film would mostly likely be derailed as sexist today and he would be displayed as more out and out villainous. Also notable is Widow Tweed and Todd. Foxes aren't common pets, but nowadays more and more people own them. Slade's distrust of Todd messing around with his chickens is understandable, but hunting someone's pet fox would be unthinkable nowadays.
Tod's mother is killed when he's only a baby, he gets chased and shot at by Chief and Slade, respectively (twice!), Copper first disowns him and then wants him dead, Tweed drops him off in a wildlife preserve for his own safety leaving him without survival skills and a friend in the world, not to mention his neighbor is a cantankerous Bad Ol' Badger. Things get a lot better after he meets Vixey, though...then worse...then better.
Tweed as well - it's made very clear that Tod is her only source of companionship, and that it's just as heartbreaking for her as it is for him, if not more so, when she has to Shoo the Dog to protect him.