"Vampire Bats and Scaredy Cats": The sudden Jump Scare of the teenage girl turning around after answering the phone and having suddenly become a vampire while her back was turned, and Shaggy and Scooby have locked themselves in the room to protect her. That damn ringing bell on the other side of the phone also falls under Hell Is That Noise. Turns out the bell is a hypnotic trigger the girl's uncle placed on her that made her slip into a state where she thought she really was a vampire.
In "To Switch a Witch", the townsfolk decide that a friend of the gang is a witch and were going to torture her to make her confess, Salem-style. Shaggy and Scooby take the brunt of this, which could have gone worse were they not Made of Iron. Sure, the squire who was the ringleader briefly apologized, but none of those responsible were prosecuted for what amounts to assault.
The Jaguaro from "Jeepers, It's the Jaguaro" is pretty tame, considering it's an ape monster with a cat's head, but the screaming sounds it makes are terrifying.
"The Harum Scarum Sanitarium" has been considered one of the freakiest episodes ever among some fans. Doctor Coffin is the ghost of a mad doctor with an evil laugh and glowing eyes.
He haunts a Sanitarium where an ambulance routinely delivers bodies and takes them away. While it’s constantly storming with thunder and lightning.
Doctor Coffin plays the organ in a creepy fashion and it makes the two attack dogs and Scooby stand up on their hind legs and dance ballroom style to the music.
The scene where the paramedics are wheeling corpses out of the sanitarium. Thankfully they're not bodies at all; it's stolen gold disguised with sheets and wigs.
The introduction of the Diabolical Disc Demon. While some may laugh at how he looks like a KISS member, some are absolutely terrified that we first see him stalking an innocent man locked in a building to do who knows what to him. It definitely doesn't help that the situation plays out like something a Serial Killer would do.
The scene where Scooby and Shaggy stumbles across a shadowy figure in the storeroom that screams bloody murder at them. Thankfully, its revealed at the end that it was just the missing friend they were looking for who had been hiding from the Disc Demon in the room and yelled to try and scare him off.
The Ghostly Gondolier is scary not just because of his creepy hooded design but the kicker reveal being that the ghost costume isn't an example of Came Back Wrong. According to the show's history shown via flashback, he looked exactly like a monster when he was alive and was even then called The Ghostly Gondolier when he betrayed Venice and led the cities enemies through its defences to get revenge on the ruler of the city. No wonder everyone was scared when that guy issued a curse.
Another moment, in the beginning, is when The Ghostly Gondolier explains his plans to the viewer with his face close up to the camera! The way he explains it is creepy because of how unexpected it was.
"The Ghost of The Bad Humor Man" is creepy because of how bizarre it is. Why on Earth would an ICE CREAM FACTORY be haunted?! The ghosts don't even have any identifiers other than being colored brown, red and white, like they correspond to ice cream flavors.
Mamba Wamba's episode has a pretty good aesthetic going for it. The Alex Super Experience uses an ancient voodoo chant as a part of their new song. This results in Mamba Wamba coming and abducting each member of the band to turn them into zombies leaving only a creepy voodoo doll in their place. All of this in a Louisiana location.
The theme music for the show gets downright creepy at times, if not disturbing. It certainly sets a darker tone much more than the other Scooby Doo themes from its time do.
The episode "Creepy Cruise" where a scientist shows off his prototype time machine to a group of investors. The time machine malfunctions and instead of bringing an object from the near past, it drags back something from the year 6,984 AD! The machine explodes, revealing a hideous, anthropomorphic insect monster with gigantic eyes from some grim distant future. Yeah, it turns out to be a hoax, but still.
The ghost of Ebenezer Crabbe from "High Rise Hair Raise", a blue-skinned man with sunken yellow eyes and a creepy laugh. What makes this episode creepy however is that during the investigation, the Scoobies visit Ebenezers now extremely elderly great great great granddaughter Nattie, who tells them that Ebenezer's ghost comes home to visit every 50 years or so, and that he should be there any moment if they'd like to stick around. Later, they're told by the construction foreman that Nattie herself has been dead for years.
The 10,000 Volt Ghost, just for how incredibly dangerous he actually is. His costume is electrified to a horrifying degree, and if he ever managed to touch the Mystery Gang, they'd have been fried to a crisp.
It's not just the costume that ups its scare factor. Its face, full of angular and pointed features resembling nothing like a human. And then there's its growl, filled with the deadly crackling sound of electricity mixed in with the threatening rumble of a furious animal bearing its fangs. Hell Is That Noise indeed.
"The Spirits Of '76", featuring the ghosts of the treasonous Benedict Arnold, William Demot and John Andre.
For those not quite initiated into the "it's always a "Scooby-Doo" Hoax" genre savviness of the classic era of the franchise, The Reveal scene in "The Headless Horseman of Halloween" where the Headless Horseman succeeds in getting a new head will be terrifying.
Although ghosts scaring the gang are par for the course, "A Creepy Tangle In The Bermuda Triangle" gets bonus points for having the weather nearly kill them all, before they even see the ghost-of-the-week. Four teens and a dog on a catamaran, too caught up in their music and food to stop and listen to the weather report, sail right into a freaking hurricane that rips chunks off their boat and nearly turns them into another Bermuda Triangle mystery.
"The Spooky Case of The Grand Prix Case" has the scene where after the ghost racer kidnapped Shaggy while his friends tried to find them and save him when they found the cave Scooby and Velma entered the cave to see Shaggy in an opening of the closet-like cave with a wall behind him and the ghost racer sealing up Shaggy in that part of the cave with bricks and cement sealing him up in his own tomb until he either starves or suffocate to death. Thankfully, Velma and Scooby ruined the racer's plan and broke Shaggy free saving him but still imagine what would've happened if Velma and Scooby had gotten there too late!
"The Creepy Heap from the Deep" has a few moments under its belt.
The monster itself, The Creepy Heap, is a yellow one-eyed sea creature with lobster-like claws and seaweed hair, and he can walk on land. His looks are pretty uncanny, and this is before we learn more about him. 100 years ago, as the legend says, he was once a sailor who was so evil, his own crewmates cursed him and threw him overboard, leaving him to drown. However, he came back wrong, and being cursed, he resorts to feeding on human souls to stay alive.
If that's not enough, the monster actually attempted to murder the gang by locking them in a room aboard a sunken submarine, which started taking in water. Fortunately, the gang had scuba gear with them and they were locked in an airlock room so they could swim up to the surface.
When the gang leaves Captain Clemens to try and call for help, the last thing we see is the captain looking behind him in fright as we hear the monster's growl. The gang doubles back when they see the Creepy Heap's footprints in the sand, leading toward the captain's house, which they just left. They find him at a table, immobile and with his frightful expression plastered on his face. On the table, a message is left on it a RED COLOR, saying "CREATURE" and "SPIRIT." That's not getting into when Shaggy and Scooby are left alone to watch him. He actually gets up and tries grabbing the two, saying in a trance-like state that he's commanded by the creature to bring him more victims! Later, it's revealed that Captain Clemens was the mastermind all along, working with the monster, an unnamed escaped convict put in prison for robbery and numerous other crimes (which go unnamed). This ruse was to keep people from learning about the captain's operation of giving criminals new identities to sneak out of the country. This makes Clemens a psychopath, especially when he and his accomplice start chasing the gang when they got close to the truth. If his threat that they would never leave is anything to go by, then it stands to reason that he was willing to dirty his hands too!
