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Nightmare Fuel: Scooby-Doo! Mystery Incorporated
This was the first episode
Quite possibly the first Scooby-Doo series that can legitimately frighten small children. The "monsters" go far beyond scaring people or kidnapping witnesses.
The intro with the Warner Brothers logo accompanied with the Looney Tunes theme done in creepy organ, surrounded by green fog, is quite nerve-wracking.
The episode title cards are on a black background accompanied by eerily serene natures sounds that have an unsettling sense about them.
The first episode's monster traps a bunch of bystanders in pods, and the bodies are so grotesque that for a while the characters think they're dead.
Episode 2 has a few scary moments, like the monster gators chasing them mostly in the dark and when one of the gators shot their arm through the floor boards and grabbed Velma's foot and started to pull her down! The way they chased Scooby into the house was disturbing and trippy, and it was earlier shown through a billboard the words "The Dog Dies". Especially since this specific line comes into play in a much later episode... All in all, the gators were some of the most violent monsters to appear on the show.
Episode 4 had the Man Crab. Sounds silly? It has the ability to pull you under the sand, making it look like you're gonna suffocate, and it emits a horrifying screech.
Not to mention that it's inhumanly strong and agile, and can walk up walls and ceilings like an insect, just look at all the destruction it wreaks while chasing people.
The zombie children in episode 5 look like they need a time out. What's even creepier - they were just normal kids going along with the promises of Que Horrifico! Those are some pretty athletic and resilient children!
In the beginning of episode 6 when Alice May pulls off her face to unveil a freaky zombie face.
Professor Pericles. He somehow caused a man to taser himself from inside his massive, heavily-fortified jail cell. And by the end of the episode, he's loose.
The Fright Hound, the shriek it makes rivals the Man Crab in spookiness. The fact that armed guards at a maximum security animal asylum unload everything they have at him and he still keeps coming, just brings the terror beyond what some might think possible for a Scooby Doo episode. Its "skin" gets shot off revealing a T-600-esque visage underneath. Did we mention it also looks like a more intimidating version of Scooby himself?
The T-600 parallels continue when it gets repeatedly crushed by heavy machinery in a factory only to continue crawling towards the gang in true Implacable Man fashion ... until Scooby drives over it with a forklift.
The Cicada Creature, made of hundreds of thousands of them, in the shape of a giant cicada. Those cicadas swarm, driving a guy in his car off a cliff, and attacking a guy while he was taking a shower. Think about that for a moment. You have bugs crawling all over you, biting and itching while you are completely exposed. *shudder*
The way the shower guy later freaked out and flatlined.
The shadows of the people in Crystal Cove as they try to capture Pericles and Scooby, as well as Aphrodite's appearance.
Episode 17, "Escape from Mystery Manor". The ruins of the Darrow Mansion are filled to the brim with Fred Jones-level booby traps, except for the fact that Danny Darrow himself used every known sharp object and weapon to try to murder his intruders, a.k.a. Scooby and the gang.
Also wondering about what Danny's fate after another earthquake splits the ruined mansion apart once again, leaving him sealed in the Earth.
And before that, Danny's description of his family passing away while he was lost in his own little world, playing with that cursed treasure piece.
Danny Darrow himself. He doesn't even look human.
Some of the more elaborate deadly traps resemble the ones from Saw.
Pretty much every chase scene. Gone are the days of Scooby-Dooby Doors and pop music being played over their chase scenes, the monsters in this series are seriously trying to hurt or even kill the gang.
There was that one time where Shaggy and Scooby tried to employ the SDD tactic on the bad guy in episode 7. Villain's response? Arson. The burning trailer they were in exploded after they got out.
Episode 10 shows that Pericles knows someone close to Fred is gonna betray them. And in episode 21, we find out from Mr. E that as long as Fred is there, the remaining 2 members won't be able to do anything. Something bad is going to happen to our fearless leader sooner or later...
The body-beast of Episode 22's monster is freaky enough by itself, and that includes the freaky mouth in its stomach...
Dead Justice. A his face is mostly skeletal with pieces of his human skin still on there, he rides a horse that would be fit for one of the horsemen of the apocalypse, his bullets, despite looking like bullet bills, are somehow still unsettling and he drags criminals off to god knows where. Granted the reveal that It was just the deputy and the criminals were most likely put in jail but he's still terrifying.
Episode 25 had a lot of nightmare fuel. Starting with the assassin Obliteratrix who is really Alice May in disguise nearly killing Mystery Inc. and Hatecraft. The fact that it was Mr. E who sent her to drive out Pericles makes it even more horrifying given that he is supposedly one of Mystery Inc's allies but that has all ways been dubious. Then we get the real whooper, the Freak of Crystal Cove. An inhuman, pale skinned, horned demonic looking monster who speaks in rhyme, not only lured the original Mystery Inc. to the abandoned church but also drove them out by threatening the lives of all the people that they loved. What makes this thing even more terrible then all the other monsters, villains, and Pericles combined is that he was the one who started it all and probably intends to end it with him on top. His chilling dialogue at the beginning of the episode and at the end leaves you with goosebumps and not the good kind.
Freak of Crystal Cove: From six to one, the spell is spun, no time to run, the curse begun
Freak of Crystal Cove: The curse begun, but soon they'll see, the buried truth will end with me. (laughs manically).
Freddie finding out that Mayor Jones is not only not his real father, but finding out that Brad and Judy of the original Mystery Incorporated are his biological parents. Mayor Jones stated that he had to stop them from coming back at all cost, even after he blackmailed them all into leaving town before, but he must have gone to amazing and horrifying lengths to separate a presumably loving couple from their child, and feeding that child a lie all his life.
How about this? Shaggy's mom states that they're going to take Scooby to a nice farm. Well, that sounds nice and dandy...if it weren't for two factors: 1) Scooby will be taken away from Shaggy while Shaggy is in military school and 2) the look in the mother's eyes and her evil smile when she says that. Think about the implications...
And that last implication is confirmed at the start of the next season. Scooby gets out of it (they sent him to the pond in reality), but how close was that?
The whole thing is messed up in the fact that Scooby didn't do anything wrong.
The scene where Professor Pericles kills Ed Machine. The way it's done, with Pericles saying "You misunderstand...I don't want to sayanything!" as shadows fall over him and the music increases its pitch...
The Crybaby Clown is rather surprisingly scary. He has a voice like The Joker's (Because it was voiced by Mark Hamill himself), with added elements of Psychopathic Manchild. Emphasis on the psychopathic. Despite babyish behaviors, this clown has shown it was incredibly malicious toward the Gang, especially in the second episode featuring him. Not to mention he blew up almost everything in his wake and managed to drive pretty much everyone out of the town until the gang got back together.
In episode 31, "The Hodag Horror", the Hodag wrecks havoc at a party the Blakes' are throwing, dragging a decent number of the guests, kicking and screaming, into the shadows. Sure we eventually find out it was only trying to steal their expensive jewelry but before that is revealed, all we hear are the guests screaming bloody murder while they are been dragged into the darkness. A scene straight out of a monster horror movie.
In "The Night On Haunted Mountain", the final shot of the episode has the Captain saying "Nibiru...", who then fades away, laughing, implying that he is a very, very real ghost.
Almost the entirety of the episode "Night Terrors". Holy crap.
The episode "The Midnight Zone" may also qualify as one of the darkest entries in the series. Apart from the "child robots," testifying to a truly deranged mind, we have not only Cassidy presumably dying, but we have Professor Pericles actively trying to kill the gang. He tries drowning them, tries getting them murdered by the robots, and attempts to blow up the base with the gang inside. And then last but not least, the dead body of Abigail Gluck: sitting in the control room, meaning she died alone surrounded by robots, a dead, decomposing body that sags a little on the chair when moved, and somehow whispers one solitary word to the gang.
Scarebear may be even worse. The villain isn't so bad when you see their motives and hear their voice (and in fact, they are one of the more sympathetic culprits in the show), but there is one part where apparently Mr. E and Pericles had set a bomb in the Destroido area, planning to kill the kids with it. Yes, Mr. E was even willing to get rid of his own company just to kill the kids and get the disk pieces. The factory with mutated animals is also quite nasty, and of course, there's the spidery-mutant avocado, which is horrible.
Anything that involves "Nibiru". Nibiru is apparently an alien being from another world who is sealed within the crystal coffin, which is the centerpiece of the "treasure of Crystal Cove". He has cursed the Planespheric Disk to corrupt people and animals with greed and drive them to seek out the other pieces of the Disk, which will lead them to the treasure, thus leading them to releasing him from the coffin. He will then proceed to make Earth collide with his home world.
In Episode 41, a real ghost tells the gang that Scooby Doo must die, because the animal companion is always is the first to act when it's corrupted by the Curse of the Planespheric Disk. And of course mentioning earlier in his warning that Nibiru gets stronger the more he is remembered...
Even creepier is hearing Friar Seras recount this to the Gang in that sinister, growling voice of his, not to mention how, after delivering his warning, he vanishes and his body crumbles into dust.
The Ghost of Friar Seras: Beware... Nibiru is coming. This has all happened before! It begins with the animal. Always with the animal! Heed the warning of the alligators! The dog dies! (crumbles to dust, a bony finger pointed at Scooby Doo accusingly)
Episode 42, "Aliens Among Us." At the end of the episode, after coming upon their first clue regarding the Cursed Treasure, the gang return to Crystal Cove to see that the City Hall (and their base of operations) is up in flames and destroyed. And it was Brad and Judy who had caused the attack in the first place.
Episode 43, "The Horrible Herd", full-stop. The Skull Cattle are monstrous, ravenous herds of bio-genetically mutated bovine drones (combined from cow, piranha, and bee DNA), eating anything and everything in sight, including reducing Crystal Cove to ruins. They only acted on instinct, and to provide for their singular queen, but it was Professor Pericles who used Mr. E's company and funds to create these horrific monstrosities. Proving once again that he is more desperate than ever to kill the gang, especially when the plan goes awry too, with Mr. E himself saying that Pericles has gone too far with this plan! He is now officially more evil than Fred Jones Sr.!
Pericles': I will walk over anyone who would get in my way of this treasure! Ed Machine... Cassidy Williams... even YOU, Ricky.
Also, the consequences of defeating the Herd. The gang capture the Skull Cattle Queen, which forces the rest of the herd to cease their destruction of Crystal Cove. They lead them all towards the ocean, and due to interference from a missile launched by Brad Giles, the net releases the Queen into the ocean, with the herd following in suit. Almost immediately after, they see the drones surface again, remembering they're part-piranha, and they can only watch in horror as they spread out through the ocean.
Shaggy: Besides unleashing an unstoppable super-predator into the ocean?
Might be averted by the fact that piranha can only survive in fresh water, and therefore the hybrid creatures would likely have died off after swimming away into the salt water ocean. And in any case, the ending of the show renders them Ret Gone.
Episode 44, "Dance of the Undead", besides seeing hypnotized citizens dancing themselves towards catatonia, having people buried alive in coffins, and seeing the kidnapped victims being dragged down into the earth feet-first, we do have another warning about the impending apocalypse, courtesy of the flatlined Nova in a raspy monotone.
Nova: Nibiru. Nibiru is coming. *lies back down*
Episode 45, "The Devouring", Professor Pericles reveals that he has injected Ricky with mutated cobra venom, which he can release in small doses whenever he feels like at the push of a button, in order to keep him in line. And remember, Pericles has already killed Ed Machine and Cassidy, so Ricky is well aware of what Pericles is capable of.
The end of the episode? Pericles' laughing insanely and saying about Mystery Inc. "We will destroooooy them!" in a creepy singsong voice.
From the opening stinger, Francilee Jackson being devoured whole by the Gluten Demon, onscreen. Though this is subverted since it turned out she was the Gluten Demon all along and staged the incident with special effects.
From Episode 47, "The Man In The Mirror", Pericles appears to know exactly that there is an interdimensional monstrosity sealed with the cursed treasure and is actively trying to find the treasure so he can free it, because apparently, the sealed creature is Pericles' master. Mr. E, Brad, and Judy seem to have no idea they're helping Pericles unleash an Eldritch Abomination onto the world.
Brad and Judy are so obsessed about getting the treasure they willingly got extensive plastic surgery to make themselves look exactly like Fred and an older Daphne for an insanely convoluted plan to trick Fred into revealing where the Planispheric Disc is.
All of the post-apocalyptic Crystal Cove. The town is in ruins with skeletons lying everywhere. Definitely one of the darkest episodes.
Especially when Fred finds what appears to be the remains of Scooby, Shaggy, and Velma. There's nothing left of them but dust and clothes.
In Nightmare In Red, we learn that those that succumb to the curse have the best part of themselves trapped in a realm between realms, and that is why Fred Jones Sr. went so bad.
In Gates of Gloom, it's shown that the closer the old Mystery Incorporated get to the treasure, the more unraveled they become. Even Brad and Judy are starting to get irritated at each other.
Look at Professor Pericles' face while he's torturing Ricky. He's enjoying it.
And the reason Ricky's being tortured? He's refusing to order the deaths of every single person in Crystal Cove, incensed at finally learning that Pericles murdered Cassidy.
The opening narrator of "Through the Curtain" by The Nibiru Entity definitely qualifies:
The Nibiru Entity: Soon... Soon, I will be free. The time of Nibiru is nearly at hand. The planets are coming into alignment, working towards my release. As are you (shot of the Mystery Inc gang about to descend into the cavern) ... Even though you know it not, I forged you. You are my proudest creation. So come now, Children of Nibiru. Be strong, and set your Master free... So that I may bathe this world, in FIRE!
Come Undone, everything relating to the Nibiru Entity.
It goes on a feeding frenzy, starting with Professor Pericles, and then going on to Fred's birth parents, Mr. E, and the citizens of Crystal Cove, including Mayor Jones, Mayor Nettles, Sheriff Stone, the Gang's families, everyone. And on-screen, no less.
At one point, it stops mid swallow to look at the Gang, and there's people hanging limply from its jaws. It's a split second but it does wonders to drive home how this isn't a typical Villain of the Week inflicted Disney Death; the Entity was killing people!