A Mouse Divided: First appearance of Friz Freleng's drunken stork character (there was a drunk stork character in Bob Clampett's Baby Bottleneck, but he was a One-Scene Wonder that may or may not have inspired Freleng's version of the character)
Tom Tom Tomcat: Hardly seen on American television due to the Native American stereotyping
Who Framed Roger Rabbit: Tweety in his original design appears in the Toontown skyline (nesting on a flagpole), and inexplicably reverts back to his original design and appears along with Sylvester in the ending.
Art Evolution: Tweety originally was a pink, featherless baby bird, but the Hays Office insisted that he don a yellow feather coat, due to objections of Tweety being "naked"—and yet they had no problems with Porky Pig not wearing pants!
In his initial appearences Sylvester was intended to resemble a baggy-pants comedian with a round belly, a low sagging pair of hips and an overly large red nose. This was toned down later, as the early design was hard to animate.
Ascended To Carnivorism: One short in which Sylvester and Tweety are Snowed-In features a mouse who hasn't eaten in so long he "forgot what food looks like." He takes one look at Sylvester and decides to have him for dinner.
Breakout Character: Both Granny and the bulldog character (later coined as Hector) made occasional appearances in initial shorts, and gradually became as much mainstream as the main duo. They are near equally prominant in Sylvester And Tweety Mysteries.
Comedic Sociopathy / For the Evulz: When Sylvester appeared without Tweety, he sometimes was made a helpless victim of an evil Villain Protagonist. In "Tree For Two", two dogs decide to beat up Sylvester for no reason, although the big one at least gets his comeuppance when he encounters a wild panther instead of Sylvester. Even more disturbing as far as victimization of Sylvester goes is the unpleasant "Canned Feud". In this one, Sylvester's owners go on vacation and forget to put him out. Sylvester finds a cupboard full of canned cat food—but the only can opener is in the possession of an evil mouse, who denies Sylvester the can opener for no damn reason, presumably to starve him to death.
It should be noted that, unlike other variations of the chase formula such as Tom and Jerry (where the cat was frequently granted Laser-Guided Karma when the victim rather than the bully) Sylvester nearly always lost, whether his protagonist instigated the feud or not. Ironically the few times he was the victor of the short was when he was dishing out the Comedic Sociopathy (eg. heckling Porky or Elmer in cartoons such as "Kitty Kornered" or "Back Alley Oproar").
In an episode of The Sylvester and Tweety Mysteries Tweety flies into a bird house restroom labeled, "Men". Tweety sticks his head out briefly to explain, "See, folks! I am a boy!"
Early-Bird Cameo: A bird identical to Clampett's Tweety in all but voice appears in "Wacky Blackout". There are also several early shorts which are considered to have prototypical versions of Sylvester.
Early-Installment Weirdness: Tweety in his earliest appearances was a sadistic trickster who actively fought back against his aggressors. Once Freleng took over direction of the character, Tweety became a genuinely innocent, very passive character.
Played with for Sylvester. His character was pretty much fully developed in his first appearance in "Life With Feathers" however as other directors took shots at the character he went through several different directions before returning to his original characterisation. Bob Clampett portrayed him as an extroverted Screwy Squirrel in "Kitty Kornered", while Art Davis used a dopier, more deadpan variant.
Flanderization: Tweety started out as a character that was cute but violent and hilarious at the same time in Bob Clampett Tweety cartoons. By the time Friz Freleng took over, Tweety was turned into a character that played cute only for the sake of being cute.
Hidden Depths: Despite Tweety becoming softer, fans still speculate that he's still a sadistic being on the inside who takes pleasure in seeing Sylvester get hurt.
Invincible Hero: Tweety. Though he had a slightly more vulnerable streak than most other Looney Tunes protagonists, he was one of very few to come out the victor in every appearance he made.
Light-Flicker Teleportation: "Greedy For Tweety" did this: Sylvester is in a hospital bed and can't move, having been given sleeping pills. Every time he opens and closes his eyes, the dog appears closer and closer, wielding a club. It's prime Nightmare Fuel.
Motive Decay: Later cartoons put more spotlight on a protective bulldog (later named Hector in Sylvester And Tweety Mysteries) who guarded over Tweety. As such more emphasis was put on Sylvester trying to dispose of the dog to reach Tweety. Some cases evolve more into a vengeful Escalating War for his constant pummellings that he seems to forget about going after Tweety (eg. "Greedy For Tweety").
Musical Episode: "I Tawt I Taw A Puddy Tat", a modern CGI short that essentially acts a music video for one of Mel Blanc's old Capitol records.
Nice Mice: Usually played straight against Sylvester with characters such as Speedy. Exceptions occur in cartoons such as "Canned Feud" and "Claws For Alarm", where Sylvester is tormented by sociopathic vermin for no established reason.
Not What It Looks Like: To avoid being blamed when another cat captures Tweety, Sylvester spent most of the episode trying to rescue Tweety from the other cat. In the end, while Sylvester was placing Tweety back in the cage, Granny reappeared and wrongly concluded Sylvester was capturing Tweety again. Quickly accepting she'd never believe the events prior, he prepares for his trip to the violin factory.
Pet Heir: Sylvester is left a fortune (and all of its attendant problems) in "Heir-Conditioned".
Ping Pong Na´vetÚ: Just how innocent Tweety is in his dealings with Sylvester is part of the gag. Granny's awareness of Sylvester antagonizing Tweety also varies from short to short.
Satan: A bulldog version of him appears in "Satan's Waitin".
Team Rocket Wins: Sylvester never won against Tweety, though got the last laugh in a handful of alternate appearances. He succeeded in eating an Asshole Victim parrot in "Catch As Cats Can" and outwitted Porky in throwing him out for the night in "Kitty Cornered".
Threatening Shark: Towards Sylvester, that is, in the latter-day short "Hawaiian Aye Aye", who tries all he can to keep Tweety safe.
Villainous Underdog: While Sylvester certainly isn't weaker than Tweety, he's no match for Granny or Hector and has to find ways to sneak past them in order to get at the bird. That's without getting into his fights with Speedy Gonzales or Hippity Hopper.
Wartime Cartoon: "A Tale of Two Kitties" has a Victory Garden appear, Tweety sics Anti-Aircraft cannons on Catsello in the ending, and tells the duo to TURN OFF THAT LIGHT.