Divergent Character Evolution: The Turtles were more or less identical in the original comics, the 1987 series gave them different colored bandanas, the toys based on that series gave them different skin tones, the movies gave them different body types that have continually been exaggerated into the 2007 movie, the Back to the Sewer redesigns in the 03 series, and the 2012 series.
Michaelangelo actually notes this in an episode of the 4Kids series: Leo takes the burden of being the leader so his brothers can do what they want: Dontaello's free to pursue his technological inventions, Raphael's free to let loose and fight, and Mikey's free to just relax because their brother's in control.
Took a Level in Badass: In all incarnations, the turtles all go through this, but Leonardo is the one who most clearly demonstrates the trope. One example is in the first season of the 4Kids cartoon where he can barely handle fighting one of the Foot Elite, and is nearly killed trying to take on all four. By the end of the fourth season, he not only takes on all four without apparent difficulty, but also bests Karai, the incumbent Shredder, in the process.
Bookworm: He seems to be this in the 1987 incarnation. In the "Leonardo is Missing" episode, he stays at the lair and reads while the other turtles go to an arcade.
Child Soldiers: Of the four, it's Leonardo who exemplifies this the most.
Combat Pragmatist: Leonardo's sense of honor dictates that he fight fairly, but when he's pushed into a corner or there is no other alternative, he will not hesitate to slice off your head.
Cultured Warrior: Depends on the writer, but if one of the turtles is going to be in touch with Japanese traditions, it's gonna be Leo.
Depending on the Writer: A lot of tropes carry over between series, but some are fairly unique. Leonardo is always the skilled, "most leader-like", and responsible turtle. But whether its accomplished by being an overly serious workaholic, a respectable older brother figure, bossy teacher's pet, meditative and spiritual, wanting to emulate fictional archetypical heroes or any combination of the above depends on the series and sometimes the story arc. Overall he is one of the most consistent across all interpretations.
One very good (actually very bad) example is the 2007 movie written by Kevin Munroe, who clearly had a favorite turtle. Not only are Leonardo's traits exaggerated and warped to provide an antagonist/foil for Raphael, but his personality and background are sacrificed for the movie's plot.
Although Leonardo's swords are often much more closely modeled around the ninjato.
Knight Templar: Leonardo's story arc in the 4th season of the 4Kids series have him nearly cross over into Knight Templar territory. His rage gets so bad he actually wounds Splinter and has to be sent away to Japan to learn from Splinter's master.
The McCoy: Though he overlaps with The Kirk. Along with Mikey, he's usually presented as the most empathic of the turtles, whether it's granting mercy to an overmatched foe, or saving the life of a mutant two seconds after she tries to kill him.
A Protagonist Shall Lead Them: Leonardo usually gets the most lines of dialogue, and most of the stories are told from his perspective. Even when he's not presented as the main character (such as the TMNT movie), he plays a major role.
Samurai: Leonardo is technically a ninja, but a lot of the tenets he quotes are in line with samurai. It's no surprise he and Usagi got along swimmingly.
Scars Are Forever: To an extent. In the Season 3 finale of the 4Kids series, Karai—whether accidentally or not—stabs Leo. Her sword goes through his shoulder and out the side of his upper shell. All throughout Season 4 the crack in his shell remains as he descends into Knight Templar territory, and even after he recovers it refuses to heal. Not until the Fast Forward reboot, anyway.
Sliding Scale of Idealism Versus Cynicism: In the 4Kids series, he starts out at the very end of the Idealism scale, even believing the best of the Shredder and then his daughter Karai. As the seasons progress he shows signs of being capable of sliding down the other way—he does this in the fourth season—though he remains mostly rooted in idealism.
The Spartan Way: All the turtles train hard, but Leonardo—whether or not by his own design—is almost always subjected to the kind that involves complete isolation, distant countries, and/or imminent death.
In the 4Kids series, Leonardo as a child was suffering from a fear of heights. Splinter brings him to the top of a gigantic reservoir and pretends to be in danger of falling. Leonardo forces himself to crawl out and save him, and apparently conquers his fear in the process.
Wise Beyond Their Years: In childhood flashbacks, he's usually the turtle acting like the adult. And for a teenager, he deals very well with duties and responsibilities most adults would be unable to fathom.
Does machines. Is the brains of the bunch. Marked with a purple headband, and fights with a bo staff.
Badass in Distress: The time he was captured by the Triceratons, and the end of the Outbreak arc after being mutated a second time. Less dramatic instances are scattered throughout the 4Kids series, too, usually when it would be easy for him to solve a problem/end an episode before its time.
Bond Breaker: Donatello was warped into an alternate future where he had disappeared for 20 years. Without his resourceful, tech savvyness, the Turtles were disbanded and the Shredder had succeeded in world domination. The supporting cast made up the last rebel resistance.
Also an example of It's a Wonderful Plot, where a character often sees that their team or the whole world is worse off for their absence.
Crazy-Prepared: "I don't know what bothers me more - that this actually works, or that Don carries around a pigeon puppet?"
Depending on the Writer: A lot of tropes carry over between series, but some are fairly unique. Don is always The Smart Guy. But he's sometimes contemplative and detached, laidback and sarcastic, nerdy and clumsy, a bit tense and highstrung, or love struck with April or some combination of the above depending on the series and sometimes the story arc.
Genius Sweet Tooth: Averted he doesn't seem to have much of a Sweet Tooth and according to his official profile his favorite food is sushi. Although in one issue of the comic comic written by Matt Howarth Donny's Acid Reflux Nightmare Is triggered by eating an entire bag of cookies.
Gentleman Snarker: In the 4Kids show, he's second only to Splinter where polite snarking is concerned.
He's more like a Deadpan Snarker in the 2012 series, particularly when he's firing back at Raphael for his "meathead" declarations.
Heroic BSOD: Like Leonardo, he suffers one in the 4Kids series' last season up until the end of episode 5. Cody finally manages to fix his Time Window to send the turtles and Splinter back to the present, but due to some inteference from Viral, Splinter is vaporized and it's later revealed that he's trapped in cyberspace.
Number Two: In the original comic series and '87 cartoon. He was expected by both Splinter and Leo to take on this role in the fourth movie, but couldn't keep Rapheal in line. By the end after Raph got his head on straight, he took over leadership from Don.
OOC Is Serious Business: Played backwards, actually. We get the 'serious business' part within the first few minutes of Same as it Never Was. Just before the episode's Bittersweet Ending, the OoC part comes in.
Took a Level in Jerkass: He was always cool-headed, but in the 2012 series, he has become more neurotic and prone to outbursts. It does work at times though. He also becomes selfish when it comes to April.
Breaking the Fourth Wall: In the 1987 cartoon, each of the turtles would break the fourth wall at some point, but Raphael did it most frequently. This is lampshaded in Turtles Forever, much to the confusion of the 2003 cartoon cast.
Brooklyn Rage: Not only because he's an angry New Yorker - the first movie even gives him a Brooklyn accent.
Deadpan Snarker: Fred Wolf cartoon. Also in most other continuities, albeit dialed down.
Depending on the Writer: A lot of tropes carry over between series, but some are fairly unique. Raphael is always the most cynical turtle. But he can range anywhere from being violent and sadistic, a sarcastic wisecracker and complainer, a meathead jock, brooding loner, or some combination of the above depends on the series and sometimes the story arc.
Lightning Bruiser: Is often noted as being the turtle with the strongest physical strength, but in the very first issue of the very first comic, he was noted as being the best at stealth, sent alone to deliver a message to the Shredder.
Manly Tears: Shows this in the "Tales of Leo" episode. The first film had him weeping over how he couldn't control his temper, and that Splinter might be dead because of him.
Middle Child Syndrome: Played with. Raphael isn't the middle turtle, but he feels as if no one understands him. Lampshaded at least once a season in any franchise. Really taken home in the fourth movie when he takes on the alias of The Nightwatcher.
Number Two: in the 4Kids and Nickelodeon series but not in others. Still doesn't stop him from wanting to be the leader and taking charge over Donatello in the other series sometimes. For example at the end of the fourth movie where Splinter outright states that Raphael has the makings of a great leader and Raph leads the rest to rescue Leo.
Is a party dude. The wiseguy. The wild one and one-of-a-kind. The most laid-back of the turtles, who lists among his interests pizza, comic books, and more pizza. Wears an orange-yellow bandana, and duels with nunchaku.
Appears in: All incarnations.
Annoying Younger Sibling: Except in the '87 series where he's second eldest to Leonardo. Leonardo listed as 16, Mike 15 1/2, and Raph and Don both 15.
Ascended Fanboy: Sorta, he's a big comic book geek who happens to be a superhero himself.
In the Mirage comics he's a comic book geek who gets to write for comic books and even becomes a published novelist.
Badass Adorable: Silly, loves him some comic books, childish, always willing to crack a joke and and can kick tons of asses with his nunchucks. Yup. Taken to it's furthest extreme in 2007's TMNT where Mikey is the shortest turtle and has huge adorable Innocent Blue Eyes (we know it doesn't make sense, but it's cute, dammit).
Crouching Moron, Hidden Badass: (4Kids series): Although he can always kick ass, his skills will occasionally take a bump as the plot requires, allowing him to take on foes that would normally defeat him or his brothers.
Big Eater: In the Fred Wolf cartoon, he'd often annoy his brothers by eating all the pizza.
Brilliant but Lazy: He's usually portrayed as having great potential, but because of his more laidback personality, he'll focus on something more fun instead.
This is enforced with his Weapon of Choice (the chucks, see below), the laziest of the turtles is the one wielding the most complex and difficult weapon. That's not something one can do without a gift for it.
Butt Monkey: Especially in the cartoons. If any of the Turtles klutzes out or has something bad happen to them for comic effect, it's Michelangelo.
Catch Phrase: The most famous "Cowabunga!" as well as "Booyakasha!" in the Nickelodeon cartoon series.
Characterization Marches On: Depending on the version, really - in the comic books, he isn't really a party dude, but more of a down-to-Earth type of guy as opposed to his brothers. He was able to author a book at one point.
In the Mirage comics he often traded back and forth with Donatello as The Smart Guy with Donny being the expert in science and technology while Mikey's specialty was culture and literature.
Ironically when compared to his later incarnations, Mikey is also one of the most violent of the group in the Mirage comics. Only Raph (who can border on Ax-Crazy) is worse.
Depending on the Writer: A lot of tropes carry over between series, but some are fairly unique. Mike is always the 'fun guy' and comic relief. But he ranges from being down to earth and artistic, to a laidback surfer dude, to an egocentric prankster, to a hyperactive ditz. What counts as the hip and coolKid-Appeal Character changes the most between series over the 25+ year history of the franchise. He's usually a reflection of the times.
Hard Work Hardly Works: Although the trope is disproved by Leonardo, there is an element of this to Mikey's abilities, and he is consistently considered to be the most naturally gifted of the turtles despite his lack of focus and dedication to training.
The Heart: Although he exasperates his three brothers on a constant level, when a serious rift between their bond takes place, he usually is the one to try and patch things up...usually via humor.
Lightning Bruiser: Michelangelo runs faster than Leo and Don and has more health than all of his brothers. However, his nunchucks are slow and have little range (Turtles in Time, The Arcade game, Manhattan Project).
Real Men Wear Pink: In Back to the Sewers he was positively delighted when April asked him to be her Maid of Honor, when people tried to call him the more gender-neutral "Turtle of Honor" he would correct them.
In the Mirage comics he was the Team Chef, even cooking an elaborate Christmas dinner in one issue.
The Red Mage: In the games, average movement speed and faster attack speed than Don, but defensively weaker than Leo.
Trademark Favorite Food: Though pizza is the favorite food of all four turtles, Michelangelo eats it more obsessively than the other three, especially in the Fred Wolf cartoon. He was the first to try it in the new show.
Taught them to be ninja teens. A mutated rat who serves as the turtles' mentor and father, raising them from when they were young. Most incarnations choose one of two origins for him: he's either the pet rat of ninja master Hamato Yoshi mutated into a humanoid form, or Hamato Yoshi himself mutated into a ratlike form.
Not So Above It All: 4Kids, but frequently displays this across all mediums. He loves his soap operas, beats out Casey and Raph in poker several times, snarks periodically about his sons' antics, and even cracks a joke here and there.
Cursed with Awesome: April is turned into a fish mutant in one episode of the Fred Wolf cartoon. She's understandably upset about it, but it saves her life when the villain's base is flooded and she's able to breathe underwater like the Turtles.
Motherly Scientist: In the IDW Comics, where she becomes quite attached to the pre-mutation turtles and even gives them their names.
Odd Friendship: In most adaptations Splinter and April strike up a deep but rather strange friendship. April is sometimes perplexed by the various personality quirks of each turtle while Splinter is exasperated having seen this all before.
The relationship is more paternal though in the 2012 cartoon.
Took a Level in Badass: In most continuities she eventually starts training with the Turtles and Splinter if only for self defense as she continues to be part of their support group. The 2012 series deserves special mention for doing this essentially right off the bat, seven episodes in.
In the 4Kids cartoon, it's revealed that the young turtles were teaching him all about martial arts and fighting (although they never found out) and each took turns to teach him what they knew. The cry comes from when Mikey was training him and told him to say "Gorogoro-sama!" (translation: Lord Thunder). But since Casey couldn't pronounce it correctly, he made his famous phrase.
Transforming Mecha: In volume 4 of the comics. Transformations include his battle form, and wings that allow him to fly.
An apprentice "Timestress" whose job it is to oversee and protect the timestream.
Appears in: Mirage comics, 4Kids cartoon
Character Development: (Mirage) Initially a ditzy, irresponsible and overly impulsive girl, she eventually evolves into a mature, responsible and self-reliant woman — after having spent some time as grim-faced, solemn and reluctant. What makes it confusing is that, thanks to her traveling back and forth through time, we don't necessarily see this development in chronological order.
In fact, we're informed that her parents originally made her take the job as an apprentice timestress in the hope that she would undergo some much-needed Character Development.
Deus ex Machina: In the Mirage comic Juliet's Revenge the fully-adult, post-Character Development Renet plays this role (having changed so much that the Turtles don't recognize her at first). For the most part, however, she averts this.
Forgotten Phlebotinum: She's completely and inexplicably absent from the Fast Forward season of the 4Kids cartoon, where the Turtles are stuck in the future — because if she'd appeared she could instantly have fixed their predicament.
Ms. Fanservice: (Mirage) About the only thing that stays consistent about her appearance is her huge breasts and tendency to wear skintight (and sometimes rather revealing) clothes.
Most Common Superpower: It's especially prominent in the Mirage comic (especially if Jim Lawson is drawing her), but the 4Kids cartoon version is notably endowed as well.
Shout-Out: The third movie prominently features a time travel scepter that looks very similar to Renet's.
A Ninja Master with ties to the New York underworld, and the franchise's most visible villain. In most incarnations, his name is Oroku Saki and he and Hamato Yoshi fought over the same woman until his attempt to Murder the Hypotenuse ended in disaster, though variations of course exist and the 4Kids cartoon notably discards that origin entirely.
Adaptational Villainy: The 4Kids version is far more malicious than any other versions. The Nickelodeon version is also a nasty piece of work.
Ascended Extra / Breakout Villain: In the very first comic, he perishes. In all other media (save Next Mutation, the third and fourth movies, and the final two seasons of the Fred Wolf show), he's the main nasty.
The Utrom Shredder was one in an alternate Bad Future. Even before that there was an episode in the 1987 cartoon with the same premise of Shredder being ruler of the world in a Bad Future, however, due to the decay he suffered in that version, he was more inept than evil on that occasion and even wanted to go to a world where he wasn't ruler.
In the real world in the Fred Wolf cartoon, however, he seemed to be quite competent as the chairman of a large corporation (Octopus Inc) which he took over, and had some success.
Evil vs. Evil: In The 4Kids cartoon The Utrom Shredder went up against The Tengu Shredder also in the beginning of the final season when The Turtles are traveling through time they come across a battle between The Utrom Shredder, The Cyber Shredder, and The Tengu Shredder. And in Turtles Forever The 1987 Shredder and Krang team up with The Turtles and Karai to take down Ch'rell The Utrom Shredder
Flunky Boss: The 2003 version almost always has some goons the Turtles have to fight through first before engaging him. In fact, almost every fight with him on his terms has him either using Foot ninjas to wear down the enemy before he arrives, or to distract them so he can launch surprise attacks.
Genre Savvy: 4Kids cartoon. Doesn't automatically assume the turtles are dead when Never Found the Body occurs, unless he has definitive proof of it. Refuses to believe a robot masquerading as Splinter will fool anyone for a second. Will put aside his personal grudge for the turtles to work alternate angles in his schemes from time to time, unless they REALLY irritate him. What prevents him from being Dangerously Genre Savvy is that he fails to recognize that both his daughter's increasing conflicting loyalties and pulling a You Have Failed Me on minions, (the same minions mind you), will eventually come back to bite you in the ass. Lastly, as Leonardo put it; "The one constant in the multiverse is the Shredder's big fat ego."
Invincible Villain: In every version, the Shredder is intially too much for the turtles to handle, leaving Splinter to save the day.
The Tengu Shredder in the 4Kids version took this to absurd levels. He can fire dark energy out of his hands, warp reality, materialize weapons out of thin air, heal himself, and transform into a dragon. Even before he turned to a life of evil, his martial arts skills were unmatched and during his first defeat, he could only be locked in a sarcophagus rather than being killed since his dark powers were too strong. On top of all that the only person who could severely weaken him to give the turtles a fighting chance was Yoshi, someone who was already dead.
Knight of Cerebus: In all adaptions except the Fred Wolf series (while still a potential threat and skilled at martial arts, he was just as silly as everyone else) and Mirage comic (which was already pretty dark).
Large Ham: Just about every incarnation of the character is.
In the Fred Wolf animated series, he is especially hammy in episodes where he is voiced by Dorian Harewood.
Multi Layer Facade: In The 4Kids cartoon, he's got a public identity which is Oroku Saki, the rich and well respected Japanese Businessman. Then he's rhe Shredder, a warlord who is using his public persona to gain power. And then his true identity originally only known by his adoptive daughter Karai is Ch'rell, an Utrom criminal who has been on Earth for over a millenium.
Omnicidal Maniac: Turtles Forever, where he's willing to destroy the entire multiverse, including himself, if it meant killing all existing ninja turtles. That includes his own daughter.
One-Winged Angel: Super Shredder in the movies and video games during the Fred Wolf cartoon era.Utrom Shredder simply has enlarged exo-suits, and the one he had in Turtles Forever could turn into a giant, Demon Shredder can turn into a dragon. In the two-episode anime loosely based on the Fred Wolf cartoon, the Shredder was also able to use the Dark Mutastone to transform into the dragon-like Devil Shredder and the much larger Dark Devil Shredder in the first episode, as well as one of the Mirror Mutastones in the second episode to become Metal Shredder.
4Kids cartoon. Overlaps with Papa Wolf, surprisingly. He seems to hold genuine concern for his adoptive daughter Karai. Until she refused to let him kill the Turtles.
In at least the 4Kids and Nickolodeon series, despite his track record for severely punishing failure Shredder often turns a blind eye to Karai's outright defying his orders, at most making empty threats about how she better not do it again.
It Amused Me: The Nickelodeon version of the character doesn't really seems to care whether what she does is right or wrong, and is mostly concerned about finding entertainment. That includes fighting with Leo but letting him leave and trying to steal a sword from a collector.
Undying Loyalty: This is, in the 4Kids Cartoon, what prevents her to make a Heel-Face Turn for most of the series; She genuinely respects the Turtles, almost has a friendship with Leonardo and knows to some extent that the Shredder's motives aren't exactly pure, but due to the role he played in her life, she feels like she owes him, and stays by his side no matter what. Even when he actually is defeated, she ends up blaming the turtles for it and going on a Roaring Rampage of Revenge against them. Eventually, it takes the Shredder trying to destroy the Universe (him included) to make her leave him once and for all.
The Vamp: In the Nickeldeon Cartoon, she has shades of this toward Leo.
Younger and Hipper: Seems to get younger in each adaptation. In the Mirage comics, she was old enough to have a teenage daughter. In the 4Kids, she appears to be a young adult; and the Nick shows, she's a a teenager the same age than the Turtles.
Mad scientist and creator of the mouser robots. Never quite seems to remain whole (or even human, in some versions).
Appears in: Most incarnations.
An Arm and a Leg: ...and an eye, and another arm and another leg and so forth...until he's reduced to a talking head in the 4Kids version.
Animorphism: His Fred Wolf 'toon incarnation eventually gets turned into a fly.
Anti-Villain: Eventually, in the 4Kids cartoon. He started out as one in the Fred Wolf cartoon but went crazy when he became a fly.
Attention Deficit... Ooh, Shiny!: In the Fred Wolf cartoon, in his later episodes he would sometimes suffer from this due to having the mind and attention span of a fly.
Body Horror: In 4Kids' "Insane in the Membrane," after four seasons of losing body parts, Baxter Stockman finally obtains a new body via cloning. Soon enough, however, he discovers that it's unstable, as his limbs start deteriorating and melting off. His mind had gone with it before being retrieved and placed back in his jar.
His fly-man form from the Fred Wolf cartoon isn't exactly pretty, either.
Butt Monkey: Gradually in both the Fred Wolf and 4Kids cartoons. The Nickelodeon cartoon does this right off the bat.
Horrible Judge of Character: In the Fred Wolf cartoon, he agrees to help Shredder even though he approaches him on the streets in his full villainous garb and it gets worse from there. Even when Baxter turns into a fly as a result of Shredder sending him to Dimension X, as all it takes for Baxter to change from wanting revenge on Shredder to wanting revenge on the turtles is Shredder telling him that it was the turtles' fault.
Implacable Man: In the 2003 version at least; Lampshaded by Leonardo and Shredder:
Leonardo: What do we have to do, to stop this guy?
Shredder: I have asked myself that question many times.
Irony: Interestingly, in the original TV Show, he ended up getting a Fate Worse Than Death, in a Lighter and Softer show, while in the darker show, not really mattering since Fast Forward still had Dark elements, Baxter gets a somewhat happier ending.
He also had shades of this in the Fred Wolf series, using the powers of the Eye of Sarnath for himself in "Curse of the Evil Eye" to get back at Shredder for bullying and abusing him, and later turning on him completely after turning into a fly mutant in "Enter the Fly".
Bizarre Alien Biology: His brain, having been scooped out of its original skull, can survive perfectly well on its own in the open air and has primitive arms (tentacles), eyes and a fang-filled mouth in its own right.
Canon Foreigner: Began as a creation of the Fred Wolf cartoon, where he merely looked like the Utroms, but has since been used in other series.
Dark Lord on Life Support: Krang's android body is a variation. He doesn't need it to survive, just needs it to survive as anything but a barely mobile brain-like creature.
Ditto Aliens: They're a race of similar looking aliens, not unlike the Utroms, in the Nickelodeon series (spelled as "Kraang").
This is actually a case of Lost in Imitation: the Fred Wolf Krang actually did not look so Utrom-like naturally; his body was destroyed, leaving him a disembodied brain, before he was exiled to Earth. His true form was... well, see Reptiles Are Abhorrent below.
Evil Sounds Deep: In the Random House audiotape versions of the Archie Comics series, Krang had a rather deep voice that sounded very similar to that of Dr. Claw's, as opposed to the higher-pitched voice he had in the Fred Wolf cartoon.
The Exile: (Fred Wolf Cartoon, Archie Comics) Part of his backstory is that he's an exiled warlord from Dimension X.
Genius Cripple: Sure, he's a genius. (His IQ is in the 900s) But as a brain, there's not much he can do on his own. Without his biosuit, he's pretty much helpless.
Jerkass / Insufferable Genius: Krang is brilliant, but not easy to work with. He insults and belittles Shredder all the time, and goes out of his way to make things difficult for his allies when he thinks he can get away with it. For example, in (Fred Wolf Cartoon) 'The Return Of The Shredder' while he allows Shredder to return to New York, but denies him any tech or help, forcing Shredder to work on his own. Then there's his reasons for preventing Bebop and Rocksteady to return as well;
"Because, I enjoy watching people and animals suffer! And you two are both!"
Reptiles Are Abhorrent: In the Fred Wolf cartoon, the episode "Invasion of the Krangezoids" shows us what Krang originally looked like — essentially a vaguely anthropomorphic Tyrannosaurus Rex with an overlarge cranium.
Karma Houdini: In the Fred Wolf cartoon, though subverted in "Leatherhead Meets the Rat King" when he ends up trapped in a cave-in, as well as in his last appearance where he is finally captured by the Turtles, and also episodes where he plays a neutral role, since he isn't really doing anything wrong then.
Those Two Bad Guys: In some of his appearances in the Fred Wolf cartoon, he teamed up with Leatherhead.
Villain Exit Stage Left: In the Fred Wolf cartoons, he would often escape after the Turtles defeated him, and it was not uncommon for him to bail out in episodes where he teamed up with other villains. Averted in "Leatherhead Meets the Rat King" and "Wrath of the Rat King".
Bebop and Rocksteady
Human gang members who were mutated into a warthog and rhino respectively, and serve as henchmen to the Shredder. Neither of them are particularly bright.
Appear in: Fred Wolf cartoon, Archie comics, IDW Comics.
Adaptational Badass: While still idiots, the IDW incarnations of Bebop and Rocksteady are noticeably far more dangerous than their 1987 cartoon counterparts.
Becoming the Mask: In the Archie comics series, the animal part of their natures began taking over more and more. This actually increased their intelligence, while also making them more neutral and less evil.
Expressive Mask: Bebop's sunglasses were sometimes depicted in this manner, most notably in the Archie comic books.
Flanderization: While they weren't exactly geniuses in the first season, they were still extreme physical threats to the turtles, especially in their second appearance after being mutated. From that point on, they became more or less ineffectual against them, and even some humans.
Friendly Enemy: In their final appearance in the Archie comics series, they hijack the spaceship used by Krang and his henchmen to reach Earth, using their guns to "convince" the Turtles not to stop them. However, Bebop and Rocksteady cheerfully accept Leonardo's request to take Krang and his goons back to the prison planet they escaped from, before returning to the Eden-like planet they've made their new home.
Race Lift: In the first issue of the Archie Comics series, Bebop's human form was depicted as Caucasian, though this was corrected in Archie and IDW's reprints of the comic. Bebop's human form was also made Caucasian for his figure in the Mutations toyline.
Tattooed Crook: In the cartoon, he sports twin tattoos of the Foot and Purple Dragon symbols, removing the former after he leaves the organization for good. In the comic books, he sports a dragon tattoo on his right arm and hand, an one of a human vertebra over his left arm and back.
Love Triangle: Is the object of affection for two suitors in nearly every adaptation. One of the suitors is Hamato Yoshi, and the other suitor is primarily Oroku Saki (though in the Mirage comics it was Saki's brother Nagi, and in the 2003 cartoon it was an entirely different character named Yukio Mashimi, who grew up alongside Yoshi and Tang Shen). She always chooses Yoshi, and the other suitor gets jealous. While there are variations in the story for what happens after that point, the one consistency is that Tang Shen always ends up dead by the end.
Missing Mom (IDW Comics): As far as is known, she is the only member of the Hamato family to not have been reincarnated.
Gender Flip: Possibly. Is male in the Mirage comic, and is referred to as male when first appearing in the 2003 cartoon — though in redesigns for the Back To The Sewers looks more female, and was even referred to as a "she" on the 4Kids website.
Team Pet: Curiously enough, subverted. He's a completely normal cat who never gets involved in the stories and whose appearances are generally spent lying around on the floor or in someone's lap.
What Happened to the Cat?: When Shredder attacks April's apartment in issue 10, Klunk is nowhere to be seen, and isn't even mentioned when April, Casey and the Turtles escape. (This is doubly frustrating because he was explicitly shown to be in the apartment in the Leonardo special, which takes place immediately before.) He remains unmentioned for several issues before he shows up on Casey's farm with no explanation at all.
Wingnut and Screwloose
An alien bat and mosquito duo from the planet Huanu
Appears in: Archie comics, Fred Wolf cartoon, Nick cartoon (Wingnut only)