[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/scooby_doo_zombie_pirates.jpg]]
[[caption-width-right:350:''And you just might die of fright! It's a terrifying time!'']]

''WesternAnimation/ScoobyDooOnZombieIsland'' is widely known for being the first (if not only) installment of the ''Franchise/ScoobyDoo'' franchise to be legitimately scary. While plenty of the later DirectToVideo movies continued the DarkerAndEdgier aesthetic, few can hold a candle to the one that started it all. The movie's tagline sums it up nicely: "''This time, '''the monsters are real.'''''"

'''WARNING:''' Spoilers are unmarked.
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* The zombies. The film pulls no punches when pointing out that they're dead, with many being walking displays of BodyHorror. There's even a scene where a zombie's head falls off and into Scooby's paws.
** The kicker: [[TheReveal Terrifying as they are, the zombies were trying to warn everyone away from something]] ''[[TheReveal WORSE.]]''
* The appearance of the first zombie: A skeleton is half poking out of the wall of a pit into which Shaggy and Scooby have fallen, then an ethereal green light enters it, causing it to wrench itself out of the wall and regrow rotting flesh. The fact that it's an angry pirate (with a rusty cutlass, no less) doesn't help matters.
** Or even worse, the cutlass might be covered in ''blood'' from the villagers he murdered before the werecats killed him.
* Simone's, Lena's, and Jacques' transformations into werecats.
-->'''Daphne:''' You won't get away with this!
-->'''Simone:''' [[WhamLine I've been getting away with it for]] ''[[ReallySevenHundredYearsOld two hundred years!]]'' ''[cue transformation]''
** While Simone and Lena being EvilAllAlong is hinted at throughout the film, the sudden revelation of what Mystery Inc. has gotten into is terrifying all on its own. They thought they were investigating more of their usual brand: things like people pretending to be zombies and using special effects... but what they got was a nightmarish human-trafficking scam run by [[SerialKiller demonic feline serial killers]] [[AndIMustScream that trap countless victims in a hellish limbo over the centuries]], along with said victims being desperate to scare away everyone before they suffer the same fate as them.
** Simone and Lena's midway state [[CatGirl are far from the cuteness normally associated with cat girls]], [[SubvertedTrope being deliberately subverted by going from conventionally attractive to terrifying]]. Their faces resemble warped, demonic versions of human faces exaggerated to resemble cats with pointed ears, fangs, and yellow cat eyes- looking like something out of a nightmare. Compared to their prior realistic, attractive designs [[UncannyValley the effect is very unnerving]].
*** Their OneWingedAngel into their full forms- they're brown-furred anthropomorphic felines but still have vaguely human faces, [[UncannyValley being an unnatural mix of human and cat brought on supernatural means]].
** Jacques' transformation is particularly [[JumpScare scary]]. Imagine this [[FauxAffablyEvil seemingly pleasant]] CoolOldGuy suddenly transforming into a [[AxCrazy roaring and vicious]] cat monster, chasing you down with every intention of killing you, either by draining your life force or simply eating you alive, as Shaggy and Scooby surely thought while running for their lives. Simone explains that Jacques wanted {{immortality}}, so they gleefully gave it to him in exchange for bringing unsuspecting victims to their island with his ferry. Once he reveals his true colors, Jacques seems much more sadistic and vicious than Simone and Lena. No doubt he was very drunk on power.
*** Right before he transforms, he tells Shaggy and Scooby (who are overjoyed to have finally run into a friendly face after having been chased all over the island for probably hours) "I'm happy to see y'all!" Jim Cummings manages to make the line sound both reassuring and terrifying at the same time.
* Just before the deadline runs out, the werecats have finally cornered the gang, the zombies all defeated, and are closing in for the kill. Even when Beau tries to fend them off with a torch, Jacques is brave and strong enough to swat it away. The way the three ''stop'' speaking English and just ominously growl as they close in, no smirk, no taunts, without any change in their expressions, is terrifying. In this moment, all of their humanity was gone and they were just predators ready for their kill.
* [[FamilyUnfriendlyDeath The final deaths of the werecats is a horror show]]. The moment they miss the deadline, their bodies begin sizzling and frying, and we see them howl, snarl, and screech in agony. They look up at the moon and are seemingly able to process that they missed their chance and are now going to pay with their lives before they really begin burning to death. We get to see the flesh vanish from their bodies until they’re left emaciated husks and then watch the fur be fried off of the skeletons, which then crumble to dust. They are completely aware and still alive throughout it, until the fur begins burning off their bodies and their eyes disappear from their skulls as they finally die; all that’s left is Simone’s necklace and scraps of their clothing. [[AssholeVictim Even so, they deserved every single second of it.]]
** The final deaths of the poor zombies as well, though this is more bittersweet considering their suffering is finally over. They decay, and the flesh is visibly torn from their bodies. Morgan Moonscar was approaching the group, but as his body began to rapidly decay, his skull just rattles in place as his spirit leaves his body. Piles of broken bones are left where the zombies once stood, their nightmare finally over.
** The fact that despite Simone’s plan being finally stopped, there was no way to save her countless victims. They truly did lose their lives and the only thing that could be done for them is to help them pass on to the afterlife.
** During this whole scene, the most powerful, nightmarish music you can imagine is playing, appropriate for the breathtaking end of such a powerful nightmare. Seriously, how did the gang ever fall asleep afterward?
* The scene where Shaggy and Scooby are nearly drained of their life force by the cat-women. As Simone and Lena sadistically grin as they seem to successfully begin their sacrifice, Shaggy and Scooby moan in pain as their faces sink in as the very life drains from their bodies, slowly becoming more and more emaciated. And they were alive for every second of it, and would’ve been doomed to remain alive if the were cats had succeeded and held them for a little bit longer. For this to happen to the two faces of the franchise, even if it didn’t take, is more than terrifying.
* Fred's, Daphne's, Velma's, and Beau's [[FacialHorror faces melting]] after their wax voodoo dolls get too close to a torch. You can cleary see the life leaving them as they melt. Thank goodness Scooby and Shaggy knocked the dolls away in time.
* The part where Fred tries to prove one of the zombies isn't real:
-->'''Fred:''' ''[trying to pull the "mask" off]'' It's the gardener!
-->'''Daphne:''' No.
-->'''Fred:''' ''[keeps pulling]'' It's the fisherman!
-->'''Shaggy:''' No.
-->'''Fred:''' ''[keeps pulling]'' It's the ferryman!
-->'''Scooby:''' [[SpeechImpairedAnimal Ro]].
-->'''Fred:''' Ah... maybe it's... ''[[[WhamShot pulls the head]] [[NotAMask clean off]]]'' [[OhCrap ...real?]]
* The scene immediately after TheReveal about the zombies is quite possibly the most genuinely fearful that we've ever seen the characters up to this point. For the very first time, they have [[RealAfterAll encountered the supernatural]] and are reacting thusly.
-->'''Daphne:''' This is more haunted stuff than I really wanted!
* The {{flashback}} revealing Simone and Lena's {{backstory}}, specifically when the pirates force their family and friends into the water to be {{eaten alive}} [[FamilyUnfriendlyDeath by]] [[CruelAndUnusualDeath alligators]]. Doesn't justify their horrific actions, but one can't help but [[CryForTheDevil sympathize]] at least a little for their tragic past and their desire (though it becomes truly monstrous) to exact revenge on the pirates.
* [[HellIsThatNoise The moans of the zombies sound pretty ethereal and very inhuman]], especially when we first meet the undead Morgan Moonscar. Becomes even more terrifying when later it's revealed that this inhuman moaning and groaning is the undead's ''desperate'' attempts to save the gang from suffering their fate.
* The sheer number of zombies shows just how many poor people had their life drained by Simone, Lena, and Jacques.
* The entire "It's Terror Time Again" sequence. This is a chase scene unlike anything before in the franchise. The usually cheerful gang who've never been in such peril are ''running for their lives'' from a horde of ''real'' undead monsters. Never before have the gang looked so terrified. And the epic song by Skycycle is an aggressive (and [[SugarWiki/AwesomeMusic AWESOME]]) assault on the senses to really hammer it home; after all these years, it's terror time again!
** Even upon re-watch when you know the zombies aren't actually trying to hurt them, it's still pretty frightening, because the quicksand, alligators, and venomous snakes they keep blindly running into as they flee are still [[{{Mundanger}} very, very dangerous]].
*** Even worse when you consider that this is probably how Simone and Lena got a hold of a lot of their victims. Either finding and dragging back people who were injured due to the inherent perils of the bayou to kill them, or opening up their arms and their home to these terrified people running from the monsters, only for them to run into a much worse fate.
** The sheer number of them doesn't help. We never get an exact count, but there's ''at least'' dozens of them onscreen; and from the fact the werecats had to drain victims every harvest moon for two-hundred years (''and'' the fact they were going to consume more than three victims between them to boot, when they targeted Mystery, Inc. and Beau), the body count is definitely in the hundreds. And way too many of the zombies rise up out of the waters and ''quicksand'', implying that much of the surrounding bayou is layered all across with corpses and remains to hide the victims.
*** Considering among the zombies are Confederate Officers from the Civil War, Simone and Lena might've wiped out a small armies worth of soldiers with no one being the wiser.
** The song itself can invoke this. It's a callback to the classic cartoon, which sometimes had songs play during scenes where the gang was being chased by the MonsterOfTheWeek. We even have a light rock version in "The Ghost is Here" (also by Skycycle) where the gang has the "investigating hauntings caused by people wearing masks" scene before meeting Lena. However, the songs in question were [[LighterAndSofter pop songs with soft vocals and light instruments]]. This time? We've got hard electric guitar chords, banging percussion and loud vocals. Even the music ain't playing around.
* The revelation that there really is a [[GodOfEvil malevolent]], or at the very least [[JerkassGods vengeful and capricious]], [[OurGodsAreGreater cat-god]] in existence that was [[GreaterScopeVillain partly behind Simone's reign of terror]].
* The vampire bat monster encountered during "The Ghost Is Here" is actually pretty terrifying... for a few seconds, when it becomes clear it's a man in a costume even before he's unmasked. He's still animated so well, has a piercing shriek, blood-red eyes, and a terrifying SlasherSmile, that you might be grateful that ''this'' monster isn't real.
* The poster itself is pretty scary. It's big in scope, with the heroes looking on at something, terrified and on the run in a spooky bayou. Meanwhile, [[EvilOverlooker some truly frightening-looking zombies are overlooking the poster from the sky]], and there's also a scary Gothic castle in the distance in front of the full moon. [[note]]While one may think that the castle will be TheVeryDefinitelyFinalDungeon, it's only featured in the prologue[[/note]] Is this a poster for a BigDamnMovie or what?
** [[https://www.imdb.com/title/tt0166792/mediaviewer/rm631686401?ref_=ext_shr_lnk An alternative poster]] isn't helping any cases either. Not only do the zombies look more terrifying, in the place of the castle is the moon with the face of a werecat [[note]] either Lena or Simone[[/note]] roaring down on the gang.
* One of the scariest aspects of the film is how horrifically [[OutsideContextProblem out of their depth]] Mystery Incorporated is. The film is essentially a group of amateur paranormal investigators in their 20s coming into conflict with a small band of [[NinjaPirateZombieRobot superpowered werecats that drain the life from their victims]], who also use voodoo magic and are backed by some kind of [[EldritchAbomination horrible cat demon or pagan god]]. Can you pull a rubber mask off of a god? No, no you can't. Even the trained police detective is unable to really help in any way. The climax of the film and the defeat of the monsters are ultimately due to the gang getting lucky against insurmountable odds.
* The subtle MotiveDecay that goes on as Simone continues through her explanation of why she and Lena are doing all of this. It starts off somewhat justified as they use their god's powers to avenge their people who died horrible deaths with [[AssholeVictim Moonscar and his crew getting punished for their crimes]], [[TheDogBitesBack with the camera angled downward to show them rising against their enemy like defensive animals rising against a hunter that goes too far]], with Simone suddenly bitter and angry about the whole situation. However, as it continues, they attack an unsuspecting plantation farmer with the camera angle [[IronicEcho with them being the predators on an unsuspecting victim]], [[HeWhoFightsMonsters becoming not only just as bad as Moonscar]], but [[SerialKiller infinitely worse]], considering [[AndIMustScream what they subject their victims to]], with the tone becoming gradually more sinister.
** What Simone, Lena, and Jascque's goals essentially are, ultimately. While it started off as a vengeful assault that was justified against their initial targets who had it coming, it quickly becomes a rejuvenation human trafficking operation where they lure victims into a false sense of security before draining them and adding them to their kills with no higher goal than just living and [[FortheEvulz sadism]]. Being the worst aspect of SerialKiller, natural predators like spiders, and demons- keep their victims in a hellish situation while they enjoy the benefits they steal from others. Far darker than anything the Mystery Inc. has faced before and it wouldn't be until ''WesternAnimation/ScoobyDooMysteryIncorporated'' that something [[EldritchAbomination much worse]] would come along.
* The Moat Monster sets the tone quite well. Even though he's Mr. Beeman, a counterfeiter, he's still out to ''kill'' Scooby and the gang such as flinging a shield at Daphne, Velma and Freddy, forcing them to run away and ''slashes Freddy's shirt'' and most likely would have attacked him had Scooby not unexpectedly dropped in (literally!).
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