Contest Winner Cameo: While there was no actual contest, Dr. Konway from "Mutation City" was based on a fan who sent the Tremblays numerous fan letters.
Keep Circulating the Tapes: No longer in effect, as Warner Bros., through their Warner Archive DVD-on-Demand program, released SWAT Kats in December 2010, with some missing scenes restored (the Episode Title Card for "The Pastmaster Always Rings Twice", and the farmer getting devoured in "The Giant Bacteria"); although in January 2012 they issued an updated version, mainly because the original DVDs had the ending credits wrong for many of the episodes.
The Other Darrin: A few characters had different voice actors between seasons, and in some cases, between episodes.
The Sergeant was first voiced by Ed Gilbert for most of Season 1. Beginning with "Enter the Madkat," however, he was voiced by Jim Cummings. Cummings voiced him for the remainder of Season 1 and all of Season 2.
In "The Wrath of Dark Kat," Al the Kat's Eye News helicopter pilot is voiced by Frank Welker. The next time he appears, in "Night of the Dark Kat," he's voiced by Rob Paulsen.
Dr. Greenbox is voiced by Robert Patrick in Season 1's "Chaos in Crystal." By the time he reappears in Season 2's "Unlikely Alloys," Nick Chinlund has taken over the role.
It isn't that Hanna-Barberahadn't done Darker and Edgier shows before, but this and The Pirates of Dark Water were the studio's first attempts at full-blown, no-holds-barred action and adventure, and they're a far, far cry from the Funny Animal cartoons they established themselves on in the 1960s. More than that, they were the studio's first truly creator-driven shows.
Elements of the unfinished episode "Succubus!" (aka "The Curse of Kataluna") were later recycled for Scooby-Doo on Zombie Island, and the episode "Eclipse" of Jonny Quest: The Real Adventures (Glenn Leopold, who wrote the episode, wrote for both of those projects; Davis Doi, co-producer of SK, also co-produced season 2 of Quest).
Show Accuracy/Toy Accuracy: The SWAT Kats action figures were all redesigned from the characters' TV versions. Most drastic change: Dark Kat was apparently a Cyborg, a revelation the show never even hinted at.
Shrug of God: Whether or not Dr. Zyme really was Killed Off for Real in "The Giant Bacteria". The writers, when asked, tend to avoid answering the question or give answers such as Glenn Leopold calling Zyme "survivally challenged" instead of dead. The closest to a confirmation comes from Christian Tremblay, who said, "He probably died!"
At the 2016 Anime Matsuri convention, a printout was provided, signed by Christian Trembley, thanking various fans for their participation in the fandom throughout the years. It ended with the apparently sincere "AND apologies for killing off Dr. N. Zyme."
Jim Cummings whenever Dr. Konway and Mayor Manx were onscreen together in "Mutation City". This probably cropped up a lot more on a smaller scale, as Cummings seemed to voice a solid third of the one-shot and background characters.
Unfinished Episode: The series was canceled so abruptly that three episodes were left unfinished; they were storyboarded and the voice tracks were recorded, but they were never animated. All three were written by Glenn Leopold.
In "Succubus!", Commander Feral begins dating the wealthy and beautiful Katrina Moorkroft, unaware she is a succubus who plans to drain his lifeforce on a full moon. The plot summary and script for it can be read here.
In "Doctors of Doom", Dr. Viper teams up with Dr. Harley Street (the MASA scientist from "The Ci-Kat-A") to create giant monsters.
In "Turmoil II: The Revenge", Turmoil escapes from prison and takes over a Kill Sat.
According to Lance Falk, a writer for the show, "When Strikes Mutilor" was supposed to end with the pacifist astronauts being human; with two of them removing their helmets and commenting how there's intelligent life, and we see an American flag in the background, confirming that the series took place on another planet in the future. However, H-B exec Buzz Potemkin "didn't get it" and had them changed to kat aliens, much to Falk's displeasure.
Lance Falk had big plans for Commander Feral in his initial pitch for "Cry Turmoil". It was originally Feral, not T-Bone, who joined Turmoil's forces. Unlike T-Bone's Fake Defector act in the finished episode, Feral's Face–Heel Turn would have been real—until he realized that the SWAT Kats were going to win, which prompted him to betray Turmoil, then claim he was planning to do so all along. In the end, only Feral and the audience would have known about his trip through the Face Heel Revolving Door.
Lance Falk had two unrealized ideas for future appearances by Rex Shard, the villain of "Chaos in Crystal". Each time he returned, he would get a different power to use against the SWAT Kats (what would have been his second appearance would have him gain power over the weather by diving into an experimental energy source, and freezing Megakat City). And each time the pilots defeated him, he'd show the effects of the previous encounter. For example:
Falk: "He’d lose an eye, so from then on when you saw the guy he had an eyepatch. And each time he comes back, he’s a little more beat up. He’s become a fanatic, and he’s lost all sight of everything but revenge, and it’s really destroying him."
The summary for this episode, titled "Cold War", can be found here. Another unused story idea of Falk's, "Blackout", can be read here.
The Villain Team-Up episode "Katastrophe", written by Glenn Leopold, was originally called "Blowout!" and was written by Lance Falk. Other than Dark Kat, Dr. Viper and the Metallikats teaming up and kidnapping Callie and Manx, it had little in common with the final product, and was a much more ambitious story than "Katastrophe" ended up being. It featured, among other things, giant tree monsters and a huge mobile command center for Dark Kat called the Fear Train. A plot summary is available here here while the script itself can be read here here.