Although he had Armodrillo since the last series, Armodrillo is shown to spin his claws like a drill in Omniverse. Giga Drill Break anyone?
In the Grand Finale, Ben weaponizes the Big Bang. That should also ring a few bells.
In "The Frogs of War: Part 2" we meet Ben's new form "Bullfrag", who is wearing some very familiar looking sunglasses (not to mention Yuri Lowenthal's character's association with a frog).
In "Ben Again", Ben admits to Paradox the idea of a Time War is awesome. Maybe minor and another thing that makes Professor Paradox a Doctor WhoExpy, but Ben's reaction might have to do with his teenage self's voice actor is admitting to being a "Whovian".
In "Showdown Part 1", Ben gives a vague explanation that he used to like Feedback so much because he felt like he was part of him. Teenage Ben and Feedback are both voiced by the same actor.
Malware is a malevolent, computer-based villain whose goals essentially amount to world domination, much like Brainiac, Superman's most well-known arch-nemesis and one of Corey Burton's most well-known roles.
In "Showdown Part 2", after being absorbed into Malware, Ben has a flashback to the past when his younger self was moping about losing Feedback. At the end of the flashback, his younger self confronts him and present Ben forgives himself for losing Feedback, thus regaining Feedback in reality and escaping Malware. This is rather similar to his voice actor's role as Yosuke Hanamura facing his shadow and gaining his Persona.
The sweater Darkstar wears as Dante is similar to one worn by Wesley Crusher.
Adored by the Network: An odd example, since Boomerang, Cartoon Network's vault channel, has slotted it in an early-evening daily slot, with extra slots on weekends. CN proper was less interested and eventually screwed it over.
Ascended Fanon: It was a common idea amongst fans that Dr. Animo's middle name was "James". Come "It Was Them", Rook refers to him as "Aloysius James Animo".
Derrick Wyatt says that the tone being closer to that of the first series was an executive mandate due to the fact that, globally, the first series apparently does the best ratings-wise.
Gwen and Kevin's "college" redesign was the only redesign they were going to get, but executives wanted them to look more similar to their Alien Force / Ultimate Alien designs for their first appearance, so they received "transition" designs for the first episode.
Derrick designed Vilgax with his respirator from the first series, but executives discarded it because they wanted the character to emote more clearly. Derrick hoped to eventually use the respirator on the design, but it never came to pass.
Eventually the executives said there were too many alien transformations, so Whampire is the last new alien the show is going to introduce.
They were also at some point "mandated to have less transformations per episode going forward."
Learning new alien's abilities. Dwayne McDuffie stated that the Omnitrix has a feature that let the bearer instantly learn the abilities of an alien they turned into (though they diverged from this rule when introducing Jury Rigg). Derrick Wyatt makes it clear that that feature is not present.
Goop's acid abilities. Dwayne McDuffie said that they were how the species digested food. Derrick Wyatt said that they were the result of an Omnitrix/Ultimatrix glitch, and are possessed by neither regular members of the species nor the Goop produced by the new Omnitrix.
Psyphon's origin. Dwayne McDuffie described him as being from one of planet Vilgax conquered, while Derrick Wyatt made a Shrug of God that he was possibly a cyborg or an android made by Vilgax.
Ben 23 was originally stated not to have have Rath, Jetray, Mole-Stache, or any aliens that Ben obtained by scanning. It's a Mad, Mad, Mad Ben World shows him to have Armodrillo, Rath, and Nanomech.
Before she even made it into the series, Derrick Wyatt said Charmcaster would not make a Heel–Face Turn and remain a villain, despite McDuffie's evident development path for her. After some fan backlash, other writers and the ending of Charmcaster's last appearance changed this answer to a "still possible".
Franchise Killer: While the show technically had better ratings than Alien Force and Ultimate Alien, its toy sales were low and the fanbase had very divided feelings on its quality. Eventually, it ended up Screwed by the Network. Tellingly, the next entry of the franchise for 2016 is planned to be a Continuity Reboot.
Many, many fans had guessed that the reason Ben doesn't use Feedback anymore was because Malware had a part in it, most guessing that he flat-out destroyed the form, which is exactly what he did in "Showdown Part 1".
Invisible Advertising: What happened to the final season; Cartoon Network had no interest in continuing the series but still had the eighth season in the can and would've been charged extra taxes if it hadn't aired by the end of 2014; the solution was to shove it of to a 10-episode two-week strip run at the beginning of November 2014 at 6 a.m., where rights to shows Cartoon Network has to air to get other properties usually are carried.
Jossed: Many figured Phil died after his first appearance in the original Ben 10 series. This series confirms that he's actually, for all intents and purposes, alive and well, albeit suffering from a split personality.
Derrick J. Wyatt got mistaken for this due to "Store 23" featuring present Feedback, despite him stating several times he wasn't in the new Omnitrix. It was actually a diffusion error: that episode was suppose to take place after "Showdown Part 1" and "Part 2" where Ben would reacquire Feedback.
He also states that Zombozo was no longer a JokerExpy. When Zombozo shows up in "Special Delivery", he still uses the same Joker-esque gadgets from Ultimate Alien rather than his more supernatural powers from the Original Series. To be fair, his personality is less like the Joker now, although it's also not the same personality he had in the Original Series.
Way Big's ability to shoot cosmic rays was stated to be caused by an Ultimatrix glitch that wasn't present in the current Omnitrix. Yet he still uses it against Malware in the arc 2 finale and has a Beam-O-War with a Waybad in the arc 3 finale.
Derrick said Steve Blum wasn't reprising any previous roles. In "Vilgax Must Croak" he plays Vilgax and in "Mystery, Incorporeal" he's also back as Ghostfreak and in the "Galatic Monsters" arc, he's back as Ghostfreak's source, Zs'Skayr.
Albedo was stated by Derrick to no longer possess the innate, at-will transformation ability gained in Ultimate Alien, instead relying on an Omnitrix again. In the show however, Albedo explains that he does still have it, and that his Omnitrix-looking device is merely a stabilizer to help him maintain his transformations longer.
"Ben 10,00 Returns" is stated to no longer be in continuity. However, while that version of Ben 10,000 is no longer treated as Ben's true future, everything else about the episode is adhered to (The Multiverse and Eon's true nature as an alternate Ben, introduced in that episode, come back in big ways in Omniverse.)
While Chromastone's flight ability and Primus's existence are said to have been retconned, Chromastone's one appearance thus far was indoors and nothing has happened with the Omnitrix that would be impossible in light of Primus's existence, though a lot of fans have wondered if we'll ever see Eunice again. It's not a contradiction because we've not seen either way, but basically... by this point it's clear that Youngberg and Wyatt didn't make a show that would make absolutely no sense at all if you missed a single Formspring post of his and were foolish enough to take past episodes into account or something, which is what many people feared would be the case.
Many aliens who were played by Dee Bradley Baker (even those who themselves were replaced by Dee) have been replaced by a different VA (such as Cannonbolt being played by David Kaye), though Dee still plays a few (Spidermonkey, Water Hazard, Lodestar.).
Meagan Smith, Gwen's 10-year old actor, is not reprising her role, meaning that Ashley Johnson is playing both versions. Despite Tara Strong returning, Johnson also replaces her as adult Gwen.
Azmuth is now voiced by René Auberjonois, having been voiced by Jeff Bennett during Alien Force and Ultimate Alien and by Robert David Hall in the original series and Destroy All Aliens. Makes sense, since Jeff's voice for him sounds like an Odo impression anyways, so it fits quite well.
David Kaye replaces Powers Boothe as Sunder. He also replaces Jeff Doucette as Thumbskull and Tim Curry as Joseph Chadwick in An American Benwolf In London, due to Tim Curry being sick at the time. He also replaces Steve Blum and Dee Bradley Baker as Heatblast and Fred Tatasciore and Baker as Cannonbolt.
Grandpa Max was recast in the French dub after the first few episodes because the original actor passed away.
Yuri Lowenthal, normally known for voicing heroic teenagers, plays several aliens that are a bit different from what he's known for. The best example is Kickin' Hawk, a much larger and more muscle-bound character than, say, Simon.
Corey Burton, well-known for playing antagonists and wise men, plays store clerk and Butt Monkey Mr. Baumman in this show.
Along with Vilgax, a role that Steve Blum reprises, he also plays Hobble, who essentially amounts to the Butt Monkey of "Vilgax Must Croak".
Tara Platt as Ester, who isn't an older, serious-minded woman.
Promoted Fanboy: While Derrick got to do some design work on the previous sequels (SevenSeven, the Vreedles), he makes it clear that he's glad to work as the main art designer on his Formspring.
Matt Youngberg as well, who was an episode director in Ultimate Alien and now is showrunner.
Recycled Script: And how. Sometimes, it really makes you feel like they took the idea to make the show more like the original series a bit too literally:
"Hot Stretch" involves aliens with high body temperature attempting to use a machine to raise Earth's temperature so it would be livable to them. Season 3 of Ben 10: Alien Force had an episode with Vulkanus attempting to do exactly the same thing with the same purpose.
While not identical, "Of Predators and Prey" has a lot of similarities with Vilgax's first direct encounter with Ben, down to Ben getting captured and the ship exploding at the end.
"Outbreak" involves Dr. Psychobos stealing a piece of the Omnitrix, resulting in it transforming the others instead of Ben. This seems like a mix of "Dr. Animo and the Mutant Ray" (where Animo had stolen the Omnitrix's faceplate) and the Ultimate Alien episode "Inspector 13" (where the Omnitrix, after being hacked by a villain, ends up turning Kevin and Gwen into aliens instead of Ben).
"Many Happy Returns" isn't a recycled script in itself, but the opening scene with Ben saving a girl from fire is basically lifted from a similar scene in episode 2 of the original show... only with Rath instead of Heatblast. Possibly a Mythology Gag.
"Special Delivery" has Psyphon trying to get his hand on a dwarf star, a device that is practically identical in its effect to the Forever King's Sub-Energy in the original show (except it works better). Plus, Ben defeats him by scaring him with Toepick, practically the same way he defeated Zombozo with Ghostfreak in their first fight. Oh, and Ben wrecked Mr. Baumann's car just like Kevin's. Seriously, it's like they tried to use as much old ideas as possible to make a new episode.
An episode has Ma Vreedle threaten to destroy Earth if he son isn't brought back to her... which was exactly the premise of the episode that introduced Attea, Emperor Milleus and Alien X.
Something Zombozo This Way Comes is almost entirely based on Original Series episode Last Laugh, down to copying the ending where Ben scared Zombozo into leaving (only with Toepick instead of Ghostfreak).
Two-parter And Then There Were None/And Then There Was Ben reuses idea of Eon collecting Bens from other dimensions from Ben 10,000 Returns, although with much greater focus.
Relationship Voice Actor: In addition to having a similar art style, Ben 10: Omniverse also shares a few voice actors with Transformers Animated. For example, Princess Attea is Sari Sumdac, Malware and Mr. Baumann are Megatron and Ratchet, Shocksquatch is Optimus Prime, and Bezel is Starscream and Isaac Sumdac.
Running the Asylum: Aspects of this show up from time to time, mostly in characterization and design aspects. Derrick Wyatt claims he and Matt Youngberg had long talked about they way they would do Ben 10 even before Omniverse, which just adds to this feel.
Screwed by the Network: The show really got screwed in its sixth season, getting bumped to a weekday 6AM EST timeslot aired daily starting on October 6, 2014 (i.e the early morning shift where it trails right after [adult swim] meaning barely anyone will be awake to catch the episodes), which saw them burn off both the remaining seasons by November.
Series Hiatus: The show had a five month break between the third and four arcs, and a equally long break between the fifth and six.
Shrug of God: In regards to whether or not Gwen and Kevin stay together and are married in the future timeline. Even the show itself portrays it very ambiguously, as they both come to Grandpa Max's retirement ceremony together but say and do nothing that would indicate being still involved.
Short Run in Peru: Most of "The Evil Rooters" arc aired in Latin America before it even had a definite airdate in the states.
Special Effects Failure: There's a sequence in "The Frogs of War Part 1" where Fourarms charges at some Inkurseans, who just stand there not firing or moving as he knocks them over.
Talking to Himself: Judd Nelson voices both Ben 10,000 and Eon. It's also a literal example, because Eon is an alternate and evil version of Ben.
Throw It In: Derrick says Psychobos' Catchphrase ("And I use the term loosely...") was originally just said once. It was when Eric Bauza, his actor, started putting it in inappropriate areas that they decided to make it his catchphrase.
Proposed names for Kickin-Hawk included Ka-Chickin and Chi-Kickin.
Zombozo's escape in "Something Zombozo This Way Comes" was to have him land on Anur Transyl, thus possibly giving him some sort of role in the arc with Zs'Skayr in it, but they scrapped it.
Molestache was intended to appear in "No Honor Among Bros," using his moustache as a weapon. The scene was cut for time.
In "Universe Vs. Tennyson," a scene of Ben using ChamAlien to spy on Chadzmuth was considered at one point, but ultimately dropped when the story was changed.
Derrick Wyatt originally planned to have the Rooters arc begin with Aggregor seeking out Kevin, revealing that he was an experiment by the Rooters to duplicate Kevin's powers.
Verdona was planned to appear at one point. A new character model was even created, but ultimately, her appearance was dropped.
Ultimate Wildmutt was considered as one of Albedo's roster. Concept art was drawn, but nothing more came from it.
Two extra fusion aliens were thought up for Ben 10,000: XLRG (XLR8 + NRG) and Gravadactyl (Gravattack + Astrodactyl). Concept art was made for XLRG, but Gravadactyl was never anything more then a "name on a board," according to Derrick Wyatt.
George Washington was intended to be travelling with a man named Ezekiel Saturday, but time constraints nixed that plot point.
Word of God: The reason why Bullfrag looks different from other Incurseans is because he's a genetically optimal (completely healthy and fit) specimen, and most Incurseans have poor diets.
Write Who You Know: Bezel's opinions on magic, at least according to the Ben 10 Wiki, echo Matt Youngberg's, indicating that Bezel was written with some of Matt's personality in mind.
Several aliens have sound effects that accompany their speech or movements: Spidermonkey has monkey-like chatter; Crashhopper's speech and jumps include cricket noises; and Shocksquatch has a crackling undertone to his voice like electricity. Liam's speech is littered with chicken noises, but Kickin' Hawk (who was based on Liam) has hawk screams instead.
We discover in one episode that Rook's given name is Blonko; his people put their surname first, like another alien species, the Bajorans. (Like most Asian-ethnic people in Real Life, as well).
Upchuck's species, Gourmands, come in two different variants, Murk and Perk. These correspond to the two different designs that Upchuck has had in the original series and the sequels. The original series' Upchuck was a Perk which is a reference to Tom Perkins who designed Upchuck in the original series, while the sequels' design for Upchuck is a Murk which is a reference to Glen Murakami who was an executive producer for the sequels. Wyatt liked both versions so he came up with the idea that there were two races of Gourmand and both were in the Omnitrix. In practice, though, aside from switching back and forth as he went among both races in the episode taking place on their planet, we've pretty much only seen the original series version.