In the first episode, Slade is seen being served tea by a butler. The Butler is named Wintergreen, and he was Slade's regular sidekick in the comics. He was most likely added to the first episode with the intention of developing into the same role in the cartoon, but was then dropped in favor of Slade working alone.
In his first appearance, Mad Mod (voiced by Malcolm McDowell) claims that "nothing teaches discipline and respect like a brain-erasing trance." Well, the line from the movie is "brain-erasing drugs," but it is a kids' show. He even uses mechanical chairs to hold his victims' eyes open.
The quote "You're just jealous cuz I sound like a rock star" is a nod to Greg Cipes' actual career as a reggae-ska rock singer.
On top of that, Cipes has lived on a vegan diet since age 8, and actually is a professional surfer, so he fits with Beast Boy's lingo.
Kid Flash is voiced by Michael Rosenbaum, who voiced the adult Flash.
Executive Meddling: Because of the Never Say "Die" trope, Deathstroke was forced to be called by his first name, Slade (except in foreign dubs). It may have been a good idea, as it is often considered more enigmatic and badass than his original name.
Could even be almost seen as an in joke, most of the first season revolves around "Who is Slade?". That in mind, try not to get a chuckle when you think that he's been running around using his real first name all this time.
Xander Berkeley as Warp, Mento and General Immortus, Peter Onorati as Robotman and Judge Reinhold as Negative Man.
Of course, the show has Michael Rosenbaum and Wil Wheaton as two of the original sidekick-based Titans from the 60's, Kid Flash and Aqualad. Not to mention the turn Speedy's VA took in playing the character in JLU, the closest the two continuities ever really got.
Michael Rosenbaum voicing Kid Flash would count as a sort-of crossover, too, as he voiced Flash on Justice League. The Flash on the show was identified as Wally West and the Kid Flash on Teen Titans is clearly based on West.
Missing Episode: "The Lost Episode". It featured a villain named Punk Rocket who used a weaponized guitar. Punk Rocket would later show up in a very minor role near the end of the 5th season as part of the Brotherhood of Evil.
Most of Gizmo and Jinx's appearances are voiced by Lauren Tom. However, the former's final two appearances and the latter's very last appearance were voiced by Tara Strong.
The Other Marty: Freddie Rodriguez originally recorded lines for Pantha, as the creative team thought it'd be funny for her to have a manly voice that was a mix of "Antonio Banderas and Ricardo Montalban". For an unknown reason, the role was recast with Diane Delano in the post-production ADR period, and she dubbed over Rodriguez' line readings. Even so, the deep voice Delano used for Pantha gave fans much confusion over whether a man or woman voiced her.
Wonder Girl (the Donna Troy version) was meant to be a part of the Titans, however she wasn't put in due to legal reasons. She did make an elusive cameo in the season 5 premiere, though, and she made a full appearance in the tie-in comic.
Slade was supposed to team up with the Brotherhood of Evil in season 5 and become a (successful) Starscream. Instead, he gets relegated to a cameo in the final episode due to the season order being cut down from 20 episodes to the standard 13 episodes.
Terra was originally suppose to be a Titan for a lot longer appearing in the filler episodes to make her feel like part of the team, to make her betrayal more of a shock, but they were crunched for time.
A crossover with Justice League was planned, but no one could come up with a good story that fit the very different styles of both shows.
Derrick Wyatt, the art director, drew characters from an obscure Teen Titans story called "Titans: Scissors, Paper, Stone", and states that he expressed interest in using them in the show. They didn't get used until a DC Nation short called "Turn Back The Clock".
Slade was gonna go by his comic name of "Deathstroke" but the censors wouldn't allow it.
There was meant to be a New Teen Titans adaptation in the early 80s but it never got past concept. It was to include Wonder Girl, Raven, Starfire, Cyborg, Changeling and Kid Flash. Wonder Girl was the leader as Robin was busy.
Executive Meddling: Arguably one of the worst victims in comics for some reason, despite only being a huge seller in one era. Virtually every single writer (since at least the '90s) has come off the book complaining about this in some way, to the point where it's obviously not just making excuses as to why their runs sucked (most of the time, anyways). The short list:
The "Team Titans", a team of future-borne characters with horrifyingly "90s" stereotypes. The Team Titans and their book were also subject to further meddling, as both Marv Wolfman and Phil Jimenez were not allowed to follow through with some plot points they'd set up by the end, or had their plans utterly changed by editorial (such as the identity of the Team Titans' mysterious leader note He was originally intended to be a 20-something Back from the Dead Danny Chase, but was made into Hank Hall to tie into Zero Hour)
The removal of Nightwing from the book and the restriction on portrayals of Nightwing and Tim Drake since the 90s, lasting up until Teen Titans volume 3. The "Arsenal-led" team was explicitly forbidden to use Nightwing; similarly, despite winning a fan contest in which he was a choice to join the Atom-led Teen Titans, Batman editors refused to honor the contest and allow Dan Jurgens to use Tim Drake in the Titans, leading to Jurgens having to substitute Captain Marvel Jr. in his place. Nightwing was also forbidden from being heavily utilized in the Jurgens run aside from limited cameos, while the original series treatment had him as a mentor to the new team.
Wildcat and Raven were also originally intended to be mentor characters, but were off-limits, leaving Jurgens to have to substitute a de-aged Atom and Lilith Clay (who took on the Raven-esque persona of "Omen").
Devin Grayson was forced to use Argent from the "Atom" team, as well as Damage from the "Arsenal" one. She also had to temporarily switch Wally West with a future Flash when his own book underwent a change.
Jay Faerber complained that he was forced to include a new team of teenage super-powered kids into the book because the editors wanted to shift the book over to a new, young cast. Eventually they kind of forgot about it as sales dwindled, so the suddenly-introduced kids got phased out at light speed.
Geoff Johns' story plans were complicated by Infinite Crisis, causing several plot threads to be rushed, changed, or dropped completely. Johns would later imply that having to kill off Superboy to spare Nightwing's life had thrown a wrench into the later plots he'd drafted. Impulse becoming Kid Flash was also a mandate by Eddie Berganza (the editor at the time) who saw it as a way to make him more of a "brand" character for the Flash family, while Johns went along with it as he saw it as a chance to mature Bart. Johns eventually bowed out of the title mid-"Titans East" arc, having only written the outlines and leaving Adam Beechen to finish up the rest.
Issue 47 was originally drafted as a story where Duela Dent got to join the volume 3 team after "Titans East", which would set her up to be a more active character. Due to the creation of Countdown and Duela being killed off to start the event, the plot was altered to be a tie-in with the Titans mourning her death.
It's speculated that Sean McKeever left the book because of this, specifically the death of Kid Devil, one of his favorite characters. A planned resurrection arc for the character was also shot down. This was, according to Dan Didio, done so as the establish the new "death is permanent" policy after Blackest Night (which didn't last anyway), but since he specifically pointed out Kid Devil, it's pretty safe to assume Didio simply doesn't like that character.
Confirmed. He tactfully calls it "creative differences".
Lobdell started out writing the book intending to carry over some themes and traditions from the old continuity. However, at some point, he was informed that this particular team had to be the first and only iteration of the Titans, it was decided that Tim Drake was always and only Red Robin, and in his Superboy book he was informed to completely reboot that character as well. The part that makes this egregious is that most of the above was retroactively added into issue reprints after the initial issues had been released and he had planted the seeds for a previous team.
The new version of Lilith/Omen was initially meant to be Raven, but Raven's debut to the new DCU would wind up delayed by editorial, necessitating the change. Lobdell also didn't want to use Trigon in his book, as he wanted to focus on new villains (and had the impression another book would be handling Raven's story), but eventually had to relent to using him.
There is a LOT of this for the series, but in a more current example: That pregnant silhouette shown in a foreshadowing page towards the end of Sean McKeever's run was meant to be Miss Martian's nemesis, Sun Girl, who would have become pregnant with Inertia's child before he died and would have sought out Kid Flash to help her raise the baby. Editorial hated the idea and nipped it at the bud.
It seems there even was a plan in place to eventually bring Kid Devil back from the dead. Unfortunately, Dan Didio nixed it, citing Eddie's death as the first example of "dead means dead" for the DC Universe. Well, until the next change in management comes about we'd suppose.
Scott Lobdell has said that Aqualad was supposed be part of his new Titans line-up, but that the idea was axed at the last minute due to the character being fleshed out in another title.