Name Drop: In "The Frickert Fracas" (Scooby-Doo Movies ep with Jonathan Winters), Maude Frickert tells Fred he looks like Glen Campbell.
A name drop through tagline: In Scooby Doo Meets The Addams Family, Scooby's "I ate the whooooole thing!" referred to the tagline of an Alka-Seltzer commercial prominent at the time, which was "I can't believe I ate the whooooole thing!"
From "The Ghost Of The Red Baron" (with the Three Stooges) after the gang sees the Baron in his bi-plane:
The Only Ones: Vincent Van Ghoul makes it clear that Scooby and Shaggy are the only ones who can get the 13 ghosts back into the chest of demons, because they're the ones who let them out.
Only Sane Man: or girl, in this case—Velma in Music Of The Vampire. Although she does get a strange snark in when Daphne disappears and it is learned that the vampire seeks a bride with "beauty and is pure of heart."
Velma: You know, I'm pure of heart. Does anyone ever think of kidnapping me?
Our Ghosts Are Different: From The 13 Ghosts of Scooby-Doo right down to the last ghost. While they are all referred to as ghosts, the series goes back and forth on whether they're actual demons or something else entirely. A couple of them even seem more like rival magic users to Van Ghoul rather than actual spirits.
Outdated Outfit: The gang's original 1969 outfits usually get copied, but a few adaptations give them fashion makeovers.
This is lampshaded in one of the made-for-TV movies. Fred is seen getting dressed, and he puts on the orange tie he wore in his original outfit. He thinks about it for a few seconds, then says "Naaah," and takes it off.
Lampshaded in Scooby Doo and the Cyber Chase where the gang meet digital models of themselves from years earlier, who are still wearing the original outfits. For most of the segment, it's the only way to visually tell the two groups apart. Fred also gives himself a comment on the ascot.
The two made-for-TV live-action obviously deviates a a little from the gang's appearances — Fred has dark hair. This is subverted and lampshaded in Curse Of The Lake Monster: Fred and Daphne pose as mannequins to lose the trail of the creature, and they are both done up as the original cartoon Fred and Daphne. After looking in a mirror, Fred thinks it's a good look. Daphne thinks he's being ridiculous.
Relationship Upgrade: Shaggy and Velma from the looks of it in the new series. Since scuttled as of episode 10, and as a result, Velma is mad at both Shaggy and Scooby.
Replaced the Theme Tune: The later seasons did away with its iconic "Where Are You?" theme song in its entirety. Many fans assert that this change coincided with an overall drop in the show's quality as it preceeded the introduction of The Original Scrappy by one season.
Romantic False Lead: In the first few direct to tv movies, such as Zombie Island and The Witches Ghost, there would always be at least one character that Fred or Daphne would have a crush on, solely so that the other wound up being jealous and inducing Ship Tease.
'70s Hair: Considering it was made about that time, it's not all that shocking.
Ship Tease: Between Fred and Daphne, so, so, so, so much.
It seems to be heading this way too for Velma and Shaggy in Mysteries Inc.
In the latest DVD movie, Camp Scare, Fred and Daphne are seen walking hand in hand into the woods at the start of the first musical number while Velma and Shaggy still have a working and platonic relationship.
A few episodes of the original serious hinted at Shaggy and Velma having a not so platonic relationship. Take her hula attempt scene at the end of A Tiki Scare is no fair, It's pretty clear where Shaggy's attention is focused and he's the only one loking in that direction. Come to think of it that whole episode (minus the parts with Fred and Daphne) counts as a ship tease. Right from the disguise gag to that scene, If Shaggy and Velma are on screen at the same time, chances are there's an incoming Shelma reference.
Spanner in the Works: Shaggy and Scooby act as this in Zombie Island; Samone and Lena dismiss them, and they end up disrupting the ritual long enough for the others to turn the tables.
Special Guest: Luminaries that appeared in cartoon form on the show: Jonathan Winters, Don Knotts, Phyllis Diller, Sandy Duncan, Sonny and Cher, Jerry Reed, Davy Jones, Tim Conway, Cass Elliot, and Dick Van Dyke. The Addams Family appearances re-recruited John Astin and Carolyn Jones as the voices of Gomez and Morticia. And Pugsley Addams was voiced by a young lady by the name of — you may have heard of her — Jodie Foster.
What's New, Scooby Doo? had guest appearances by hockey's Brett Hull, baseball's Mike Piazza, skateboarder Chris Krug, Steve Harwell of the group Smashmouth, and music group Simple Plan. Episode 11 of Scooby-Doo! Mystery Incorporated featured author Harlan Ellison.
Speech-Impaired Animal: Lampshaded in Scooby Doo and the Alien Invaders; Crystal and Amber [Shaggy and Scooby's love interests in that film] are revealed to be aliens at the end, and Amber, the dog, can talk.
According to studio bios from the cast we know, Fred and Shaggy are 17, Daphne is 16 and Velma is 15. A Pup Named Scooby-Doo would chronologically have Fred and Shaggy at age 10, Daphne at 9, and Velma (who in this series sleeps in a jumper) at 8.
Stalker with a Crush: In What's New, Scooby Doo?, Velma has one in the form of an inventor nerd named Gibby Norton.
In "Bravo Dooby Doo," Velma flirts with Johnny Bravo.
Velma: (winks to Johnny) I don't bite!
Johnny: (points to Daphne) Yeah...but does she?
In Scooby-Doo: Camp Scare, a ranger investigating the destruction of Camp Little Moose flirts with Velma, who is squicked.
The Stoner: Shaggy. Okay, so the show never actively says he's The Stoner but he's stick thin, scruffy, always hungry, will eat dog snacks, thinks his dog can talk (the others could be humoring him or are probably as wasted as he is), and he's always freaking out. Who cares if the show never dared to canonise it?
Only creators Joe Ruby and Ken Spears could vouch for it. The show was created for the 2-11 age bracket on Saturday mornings after all.
According to the show's creators, the idea that Shaggy did pot never even entered their heads in the creation of the character. But since it was brought up, a lot of the movies have a tendency to joke about it. And fans believe it.
Story Arc: "Scooby Doo: Mystery Incorporated" has one of these, with the mysterious Mister E sending them clues about their latest mystery and challenging them to solve the disapperance of a previous band of mystery-solving teens years ago.
In the movie Looney Tunes: Back in Action, Scooby and Shaggy are seen in a studio cafeteria threatening Matthew Lillard, who played Shaggy in the 2002 and 2004 live-action Scooby theatrical feature films (averted seven years later, when Lillard would assume Shaggy's voice on the cartoon).
Shaggy: What kind of performance do you call that? You made me sound like a total space cadet, man!
Matthew Lillard: I'm sorry you feel that way. I was just trying to be true to your character.
Shaggy: If you, like, goof up on me in the sequel, I'ma coming after ya!
Scooby: Reah. And Ri'll rive you a Scooby Snack! [growls viciously]
In "Curse of the Lake Monster" the jab about relationships in the end seems to be one directed towards Mystery Inc.
Take the Wheel: In Monsters Unleashed, when the gang is being chased by the pterodactyl monster, Freddy asks Shaggy to take the wheel of the Mystery Machine while he tries to shoot the monster down. A little while later, Shaggy gets called to the back of the van so he can help Velma, and he leaves the driving to Scooby. To Scooby. Granted, he's pretty intelligent as far as animals go, but he's still not that far up the scale...
Tangled Family Tree: Each series/spinoff seems to insist on introducing (and, with few exceptions, never showing again) more and more relatives of the gang... cousins, uncles, aunts, grandparents, parents (Fred's and Shaggy's parents in Mystery Inc. are different than was previously presented), and in some spinoffs, even siblings. At this point, the Rogers, Dinkley, Blake, Jones and Doo family trees' must rival the (Mc)Duck family tree in complexity...
Taxman Takes The Winnings: This turned out to be the motive behind one of the Monster of the Week schemes. The perpetrators had discovered a sunken treasure, and were trying to smuggle it out without declaring it, because if they did Uncle Sam would come in and take more than half of it.
This was most likely comic book story "The Galleon Ghost" (Gold Key #2, June, 1970). The "ghosts" were actually gypsies who feared that the IRS would take it all, but Fred assured them that they would still be well off after Uncle Sam's take.
10-Minute Retirement: Happens twice. In the prime time special Scooby Goes Hollywood, he quits his Saturday morning show to pursue a career in nighttime TV. In the 13 Ghosts episode "It's a Wonderful Scoob," he becomes so traumatized by the episode's Big Bad that he goes back home to his parents. In the first instance, Fred, Daphne and Velma lead a rally for Scooby to return to his cartoon show. In the second, Vincent Van Ghoul shows Scooby the future world without him stopping the villain Time Slime.
There Are No Adults - They either don't have parents or their parents just don't care that their teens travel around the world solving mysteries with a talking dog.
Mystery Incorporated subverts this, with their parents appearing frequently to try to get them to stop solving mysteries, because in this world that's what rebellious teens do apparently. Except for Velma's mother who provides them with information on whatever monster concept the crook of the week is using and her father who only appears three times.
Those Two Bad Guys: Bogel and Weerd from The 13 Ghosts of Scooby-Doo, a pair of bumbling ghost minions who bounce their services from demon to demon, but consistently mess up.
Toilet Humor: Shaggy in Legend of the Phantosaur when the biker picks him up:
Shaggy: And there goes the bladder!
Took a Level in Badass: Daphne in the current run of feature-length cartoons, What's New and the live-action films. While sometimes still filling her classic damsel role, she now has martial arts skills, frequently gets the gang out of trouble by MacGyvering their way out of a trap with items in her purse and generally seems no more helpless than Fred or Velma.
It happened even earlier than that. In The 13 Ghosts of Scooby-Doo, she turned in her purple dress for a jumpsuit and went off with Shaggy and Scooby to hunt down actual ghosts.
Shaggy turns it up to eleven in Legend Of The Phantosaur, provided the key word is given to him at the right time.
Vague Age: The Mystery Gang. They're only described as "Meddling Kids," but considering how much time they spend on the road, they almost certainly have to be in their 20s, or late teens at the youngest.
Their ages have been given, for the original series at least. Velma is fifteen, Daphne is sixteen, and the boys are seventeen. The original premise was to have them be a teen rock group on tour, which makes the lack of parents and time on the road more explainable.
Verbal Tic: Like, Shaggy, obviously. Also of note, Professor Flakey in 1972's "The Caped Crusader Caper", one of two crossovers with Batman and Robin. Flakey's dialogue consists almost exclusively of spoonerisms and this memorable malapropism:
Flakey: I always liked Shaggy because he's dumb to kind animals!
Video Wills: The phonograph record in "A Night of Fright Is No Delight".
The Walls Are Closing In: In "A Night of Fright Is No Delight", the gang discovered a locked trap door and a nearby organ that appears to control it. Scooby offers to play the organ to see whether they can open the trap door, but when that happens, the gang realizes the walls are closing in on them. As the gang tries to hold the walls back, Scooby desperately plays the instrument more, and then frantically dances on the keys to try to get it to stop the walls, and succeeds by sheer luck.
The message on the sheet music read, "Feed the organ and watch the floor," and Velma deduced that it meant the musical notes F-E-E-D, which she plays and a panel in the floor opens. As to which keys Scooby pushed to stop the walls, that is anybody's guess.
Scooby Doo: Music Of The Vampire: Shaggy and Scooby are told by swamp hermit Tulie that his prototype for hovering shoes was stolen by the vampire. When the gang catches the vampire, this is never brought back up. Likewise, we never see Jasper Poubelle and his vampire-hunting posse at the conclusion.
Who Is Driving?: Zig-zagged twice in the episode "Foul Play In Funland." First, Velma and Scooby are in a runaway bumper car which Velma can't control after losing her glasses (and she even taps her foot on the floorboard searching for a brake, which bumper cars don't have). Then, the gang is helping Mr. Jenkins find his recalcitrant robot in a jeep, which Velma's driving. She's only fifteen! Does she have a permit?
And after the ride in the bumper car, where is Scooby sitting in the jeep Velma is driving? Shotgun!
Velma does show some mad skills with the Mystery Machine in Scooby Doo: Music Of The Vampire.
Daphne:(having just overpowered Zarkos) Now who's the damsel in distress?
Daphne: Straight up!
Who Would Want to Watch Us?: In Scooby-Doo and the Cyber Chase, the newly redrawn cast mock their original appearances in a video game based on them. (Cyber!Shaggy, however, is wearing his red shirt from a couple of the movies.)
Why, Thank You, X!: This happens a lot in Scooby-Doo, especially when Scooby and Shaggy decide to cook or just fool around after splitting up. The monster/ghost makes an appearance handing them something or offering a suggestion before they see it and run for their lives.
It also happened to Velma when she was in a college lab testing a mummy's bandages to find out if they were really ancient and the mummy handed her a test tube with the right chemical in it. (In retrospect, it's also kind of a clue that the mummy is one of the professors.)
Wild Wilderness: Well there are several locations from swamps to forests to islands to...well you get the point. They have to many adventures to really point this out to often but this trope swings in and out often.
Would You Do It For A Scooby Snack?: Normally with Shaggy and Scooby, but when Velma is offered a Scooby Snack in "A Terrifying Round With A Menacing Metallic Clown" to act as bait to catch the monster clown with Scooby, she refuses saying "I may be scared, but I'm not desperate." But she changes her mind when Daphne offers her a CD-ROM of the Encyclopedia ("King Tut, you're back in my life again!").
Writing Indentation Clue: One episode has Fred, Velma and Daphne come across someone's diary whilst looking for clues. They find that the ink of the text has faded, but the pressure of the pen has worn through to the next page. So one of them grabs a coal and shades the paper to see what was written.
Not to mention that there were never any witches burnt at the stake in America. They were either hanged, crushed with stones, or sentenced to imprisonment.
Younger than They Look: They look like teenagers to you? Possibly lampshaded in the Valentine's Day special of What's New, Scooby Doo? where a flashback shows a much more teenage-looking Shaggy breaking up with his then-girlfriend. (It's a little subjective, but the beginning of Zombie Island heavily implies the characters are now college-age and subsequent animated versions of the franchise usually seem to tacitly follow suit even if the continuity is often vague...)