- Many times, especially loud Screamers are used to indicate when characters get scared or in pain. Watch out!
- The many times when characters contort their Gmod models to exaggerated amounts can count as this.
- Many characters have been subject to Sanity Slippage. Seeing a usually nice character become enraged or resort to extreme methods to get their way is jarring.
- Many of the villains, despite or even because of their comical nature, can be potentially seen as unnerving if analyzed at a different angle.
Bob: I'm a good boy who has never done anything wrong. Except for the murders...
- SMG3, the main antagonist of the series after Bowser's HeelFace Turn, is usually portrayed as comical and bumbling. However it doesn't keep him from being the most dangerous threat to the main cast and would've beaten the heroes several times if not for sheer luck. His schemes most likely could have dangerous effects if applied to real world terms as well...
- Enzo and The Villager were both Ax-Crazy Serial Killers who, while they didn't have the most relatable of motives, still had a very respectable list of offenses.
- Ztar, the series's first true Knight of Cerebus, caused destruction to nearly the entire world in only his 2nd appearance.
- Weegee can be terrifying when angered, but can be pretty friendly and knows how to have fun. Said way of having fun also includes destroying a city through a piggyback ride..
- King Pipe nearly infested the Mushroom Kingdom with several pipes, and likely would've killed Mario, Luigi, and SMG4, had Mario not taught him how to be a plumber, convincing him to let them go.
- Grand Dad was a borderline Reality Warper, turning nearly the entire Mushroom Kingdom into a mess of bootlegs and glitches.
- Saiko Bitchitaru, prior to her HeelFace Turn, was certainly capable of causing mayhem, but it was taken up to its height in "Final Fantasy Mario", where she not only commands an army, but has access to a surplus of deadly technology.
- Waluigi, after discovering the Power of Rejection and being denied entry into Super Smash Bros. as a fighter once again, went completely mad. His first villainous action? Infect the entire Mushroom Kingdom with a zombie plague that nearly succeeded in zombifying everyone. Even then, it got everyone to reject him, fueling his powers even further. He shows a downright scary level of competence and determination in seizing power, and will not stop until he's accomplished his goal of making everyone feel as he has. Even after he was depowered and underwent a HeelFace Turn. he still has access to these powers.
- Though Bob isn't a full-on villain, his monotone voice, willingness to betray his "friends" and some throwaway lines that portray him as a murderer can come off as creepy. It gets worse whenever he randomly lapses into Soft-Spoken Sadist speech.
- Francis, the leader of the Anime Cartel, is possibly SMG4's first twist villain. He's also the villain who's taken most seriously, and is seen by many as the most depraved of all of them. He seems okay at first, since while the Anime Cartel were shady enough for even Tari to not trust them, he doesn't do anything particularly villainous, he listens to Saiko without question, he seemed to care about the rest of the Anime Cartel, and he willingly helps Mario and Co. get anime unbanned. But then, out of anger that Axol didn't draw him any waifus with his magic ink weaver, Francis decides to take it for himself, imprisoning Axol and kidnapping almost all of Inkopolis in order to use the former's pen to make all the waifus he wants—something that would kill the Inklings. What really cements him as a villain is having one of his drawings impale Desti, thus making him responsible for SMG4's first major Character Death, giving out a manic laugh while it happens. Looks like Tari was more right about the Anime Cartel than she thought.
- "Luigi's Retarded Manson". While it is very funny, the castle (that Luigi is trapped in) has a sinister feeling and a very dark atmosphere. You just don't know when something is going to pop up.
- Most of "The Forgotten Door".
- "The Visitor" (2014):
- The Scare Chord and the Groin Attack-like sound effect when the shady Serial Killer kills Toad. Same as with Luigi.
- The entire scene where the killer is shoving characters in toilets is enough to make your heart pound faster. The moments where he throws them into the toilets aren't shown either, which makes it more terrifying.
- Heck, the whole scene is a blatant reference to the 2011 blooper of the same name and with a similar plot.
- When Enzo approaches Mario and SMG4 before SMG3 attempts to kamikaze into him; complete with Freddy Fazbear's theme from Five Nights at Freddy's.
- "SM64: Halloweegee special 2014":
- "Freddy's spaghettiria":
- Golden Freddy's Jump Scare. The giant Toad face says it all.
- The ending of Mario's dream about the SMG4 version of the Bite of '87, in which Toad runs up to Mario, who has the body of Foxy, screaming nonsense and angering Mario so badly that Mario climbs down from the stage and slashes off a piece of Toad's head. The entire building suddenly erupts into chaos. Mario doesn't care.
- The entirety of 5AM. Mario starts losing it after spending the entire night dealing with the animatronics. Meanwhile, in the bathroom, Chica is alone until Foxy barges in and tells her "the pizza's ready!" Chica goes into the dining area, only to find a plate of spaghetti instead. Chica eats it anyway, but spits it out saying "That tastes like shit!", which makes Mario finally snap. What follows is a Roaring Rampage of Revenge that ended in Mario giving Freddy the same Jump Scare he gives many players, with a huge mouth to go along with it (although there's Nightmare Retardant if you listen closely and hear "pingas" repeating in the background).
- Hope you don't find that face disturbing because Mario now has that expression nearly all the time in recent videos.
- "Princess Capturing Simulator": Bowser's Mushroom Samba face◊ could give Mario's Nightmare Face a run for its money.
- Toad's situation as revealed in Meet the Toad. He's essentially the only sentient member of his race and can't leave the castle and its wacky antics. As a result, he resorts to candy to ease his pain.
- "How to catch Pokemon" is a generally lighthearted episode, but how does Mario finally succeed? He gets a Mimikyu. Doesn't help that the video ends with him removing its hood.
- In the same episode, Mario attempts to catch one with a bear trap and spaghetti. When it inevitably backfires, he does live, but which Pokemon was close to falling victim to the trap? Sylveon. Mario very well could have KILLED it.
- Stupid Mario Party brings back the Koopa Bank from Mario Party 2 onwards. That's a nightmare in itself. However, SMG4 thought it was a brilliant idea to portray the owner of said bank with an Off-Model Slasher Smile uttering "Money..." in a sinister voice and lunging at Mario, eating his head (and costing him 5 coins, of course).
- At the end of "Welcome to the Kushroom Mingdom", when Toad puts on the gnome hat that fell out of the portal, he turns into a gnome and turns around to face the viewer with a Uncanny Valley gnome face, complete with Scare Chord (although the blow is softened by the random shout of "AH'M GAY!").
- The end of "Marioception" where Mario has a series of Dream Within Dreams in increasingly Bizarre Nightmare Sequences while Mario in real life shakes around terrified and miserable because Toad and E. Gadd are using the dream invention on him as vengeance for Mario stealing it and E. Gadd's chocolate. Even if it's supposed to be karmic it's a bit excessive, and it's possible Mario was dreaming the events of the whole video and didn't actually do anything.
- In SMG4 Christmas 2017: The XMAS Discovery, we get to see Meggy truly pissed off for the first time ever. And my God is it terrifying, not only does she uppercut Waluigi through the roof, but then proceeds to try to murder Wario by using Christmas tree stars as shurikens, and then one hits the emergency button, causing barriers to block Wario from escaping.
- In Doki Doki Mario Club, seeing Fishy Boopkins doing a pagan ritual to make Saiko come to life is a bit... disconcerting. Of course, it's still better than the behavior of Saiko herself, who makes Monika look tame by comparison.
- One could still feel sorry for Saiko since prior to her release she was just a game character trapped in a laptop.
- Remember a certain Signature Scene at the end of Avengers: Infinity War? Well, "The Super Dudes" contains a horrible Shout-Out — when Wario uses the Power Glove to nearly inflict Cessation of Existence on Mario, Bowser, Fishy, and Steve.
- In Waluigi's Time, the entire concept behind The Power Of Rejection - the power to inflict the pain of all the rejection you felt throughout your whole life, turning those affected into crying messes unable to defend themselves. Imagine the potential... What if someone truly evil like SMG3 had it? Or Saiko?
- Worse, Waluigi was rejected for Smash Bros and relegated to being an Assist Trophy AGAIN at the end of the episode, and it seems to have pushed him over the edge.
- The victims of the T-Pose Virus in Mario and the T-Pose Virus act very much like one would expect from zombies straight from World War Z: unthinking monsters driven only by the urge to reproduce (as in infect other lifeforms with The Virus) that take a hell of a lot to put down. And then The Mario Convention turned them into even more Nightmare Fuel, because they can no longer be cured.
- Particularly creepily is how Meggy gets turned: after knocking over four T-pose zombies, they just slowly get right back up with no change in expression and without even moving their limbs and then proceed to tear Meggy a new one and turn her into another zombie offscreen.
- After Luigi gets turned, Mario goes into a (relatively) quiet rage and kicks Bob (the reason why Luigi got turned in the first place) off the roof they're on and kills him (not for real) in a scene lacking in the humor that SMG4's content is typically rife with. It's a startling out-of-character moment from Mario that makes something perfectly clear: he may not be the best brother to Luigi, but if you cause fatal harm to his little bro you will not be getting away scot-free.
- The ending of this video, in a rare moment of continuity, also follows up on a creepy moment from Waluigi's Time. Waluigi, armed with his Staff of Rejection, was the one who gave Shroomy the T-Pose Shroom for him to eat in the first place, showing that the entire preceding video was his Start of Darkness. Waluigi has gone from a sympathetic "loser" to a maniac hell-bent on causing as much chaos and destruction as he can to the ones who he feels wronged him and is now an Arc Villain for the SMG4 universe. All because Master Hand wouldn't let him be a fighter in Smash Bros. and relegated him to Assist Trophy status.
- Mario SAW further expands on this with all new implications. Not only was Waluigi expecting the outbreak to be stopped and his role in it exposed, but he was also counting on it. The Power of Rejection grows stronger with each person who hates and rejects him, so with a single plot, he turned almost the entire kingdom against him... except for Mario. And with Mario now rejecting him as of the end of Mario SAW, Waluigi has now ascended to what he calls his "final form" (which is really just his buffed up Rambo body with a comically tiny cape, but still).
- While "The Mario Carnival" is otherwise a purely comedic episode, early on Bob makes an offhand comment about how Wario hasn't been seen or heard from since the events of "Waluigi's Time", suggesting that Waluigi has done... something to him. This is mitigated in Mario The Scam Artist, where it turns out that Wario went missing because he's searching for Waluigi.
- After Mario SAW came out, fans found to their horror that Waluigi was now on the channel banner. Each subsequent video leading up to "War of the Fat Italians 2018" had Waluigi getting closer while everything else on the banner slowly became distorted and vanished. The last one before "War of the Fat Italians 2018" was just Waluigi in his final form with a purple, spiraling background. Nothing else.
- The Mario Convention started off like any other SMG4 episode, with the cast going into different shenanigans around a convention center. Then Mario and Meggy decide to get an autograph from Hideo Kojima for their friends. Mario wins and gets something handed to him... a T-Pose Mushroom. Meggy pushes him out of the way and gets herself infected and Kojima turns out to be... Waluigi.
- Waluigi became powerful enough to take control of anyone he chooses. He demonstrates this to almost everyone at the convention center with an evolved T-Pose virus. Oh, and there's no cure AT ALL. (Until his staff gets broken in War of the Fat Italians 2018.)
- Waluigi easily subduing Master Hand, one of the most powerful characters in the series, while using Mind Control on him to make him a part of his army is both as impressive as it is scary. What's even more horrifying is the accompanying cracking sounds while it's happening, leading you to believe it's something else entirely at first.
- Tari's position isn't one to scoff off either. While she is out of sight and behind a hiding spot, she is still Alone with the Psycho, with no possible escape route in sight. Said psycho has also pretty much killed her best friend, and incapacitated Master Hand, who's also the closest thing this universe has to a God.
- Mario and the Waluigi Apocalypse gives us the current state of the world after the apocalypse. It's... not pretty to say the least.
- Meggy can only shed a tear as Tari tries to get her back to normal. So the victims are left entirely aware.
- The ending of the episode is way different from the normal one. We have Waluigi's symbol replacing the SMG4 logo and dark music in the background...
- Fishy Boopkins Plays VR Chat starts off like a normal Filler episode, chronicling what exactly Boopkins is doing during the Apocalypse. Things take a darker turn though, when towards the end, Boopkins answers the door to his house and finds Waluigi, who proceeds to infect poor Boopkins. Worst part is that we don't see it happen, we just hear Boopkins's cries of terror and the VR system fizzle out, with bleak music in the background to all of this too.. And there isn't even a usual ending to this.
- If Mario was in... Starfox is mostly a lighthearted comedy adventure as per the standard SMG4 style, but it also introduces the idea that memes are a Cosmic Keystone in the SMG4verse, and a planet without memes will completely cease to exist. We are thankfully not shown the end result of overexploitation of memes, but it still leaves a chilling potential that a future villain could use this to cause mass pandemonium.
- The Mario Purge in almost its entirety.
- For 12 hours, all crimes committed by Teletubbies are legal. The implications are disturbing, to say the least.
- The Teletubbies embody pretty much every horror movie trope when going after Mario and Co.; going so far as to kidnap and attempt to murder them. Including a child (Boopkins). And they'd have gotten away with it, due to the laws of The Purge.
- Mad Mario takes place in a post-apocalyptic wasteland, brought about by a shortage of internet. It's horrifying to see several of the nicer characters such as Meggy and Tari take a level in jerkass in the video.
- The end of the Bob's Mansion blooper. Just who is the mysterious character holding the controller? Why do they have a cybernetic arm like Tari? What are they doing? The end of "The Mario Concert" seemingly reveals another character with a cyborg arm, apparently screwing it on. "War on Smash Bros Ultimate" reveals a third new Cyborg.
- Turns out it was a teaser for a new series that was being worked on. Doesn't make it any less creepy out of context, though.
- The ending of "The Mario Concert" is a mixture of this and Tear Jerker. After Fishy Boopkins accidentally ruins Bob's rap concert, he tries to go and apologize to him, only for Bob to refuse his apology and then continue to berate him for trying to help him (not at all helping is the fact that he also has visibly angry eyes for the first time ever). And where one might think he was just angry over his chances of success being ruined, he then, out of nowhere, reveals the truth about the past few episodes and goes into detail about how all of the events were engineered and his compassion faked so he could manipulate himself into a successful rap career. It's been Hidden in Plain Sight the whole time in the form of good old SMG4 antics, but it is here that the truth about him is finally shown to be worse than anyone could ever imagine.Boopkins: I wanted to say I'm sorry for what happened. I know I shouldn't have gone on stage, but... it really did sound like you needed help.
Bob: You think I needed help?
Boopkins: Well, yeah, I just wanted to-
Bob: I was doing amazing! No, I was doing better than amazing! I clearly told you to not interfere and now my rap career is ruined! I tried so hard to get to where I am now, and now it's all destroyed because of you. To think... the lies I told... The scams I had to pull to get here, and now it's all gone. I even pushed you down a well for god's sake!
Boopkins: What? You pushed me?
Bob: You didn't fall down there by accident. I pushed you down there, just so I could be the hero and save you. It was the perfect chance to push my rap music!
Boopkins: You mean... you didn't save me because we're friends?
Bob: Hell no!
Boopkins: [breaks down crying]
Bob: I even hatched a brilliant scheme of Bobsgiving where I: replaced all of the fire extinguishers in my house with flamethrowers; asked you idiots to go and get some gasoline I labeled as "Bob juice", and told Meggy to go help cook knowing very well that klutz would burn down the house. Just so the house could blow up and I could use the sob story to skyrocket myself to fame.
Boopkins: [in tears] Bob, that's not nice!
Bob: Nice? You think this world is nice? You're either an asshole or a pushover: a Bob or a Boopkins, and I sure as hell don't want to be a Boopkins. I'm done with you. I don't need anyone. I'm gonna build my rap career... bigger this time.
- "Mario and The Diss Track" follows on from the above, and expands upon it with the reveal that Bob merch is everywhere AND the entire Mushroom Kingdom has become devoted to him! Even the rest of the main cast aren't immune, not even paying attention to Luigi trying to warn them about Bob's betrayal OR any attention to Boopkins and his Heroic BSoD until Bob disses them.
- "If Mario was in... Deltarune" has the heroes encounter Jevil, who is just as insane as he was in the game. Unlike the source material, his claims of "I CAN DO ANYTHING!" seem to be true here. He turns the battlefield 3D (and Ralsei and Susie into GMod models), teleports and spams projectiles, all while doing Fortnite dances the entire time. He can even summon objects from other realities. It's scary to think what would have happened if Mario hadn't tricked him.
- "Mario's Prison Escape"; the Guards are reintroduced to the main bloopers. Despite the comedic back-and-forth banter and stupid remarks, Swagmaster of all people proves to be the biggest threat throughout the video; attacking Mario and co. with an ax several times, coming after them in a military jeep, taking out the group's getaway vehicle, and showing no hesitation in shooting everyone with a rocket launcher.
- "Mario's Illegal Operation" reveals that Peach has illegalized anime following the events of "Mario and the Anime Challenge" when Mario, Boopkins, Bob, and Tari's anime challenges caused major damage. The state of the Mushroom Kingdom is bad, with the Anime Secret Service (A.S.S) setting up anime checkpoints and "yeeting" anyone caught with anime, crime cartels being set up everywhere and anime being publicly burned.
- The ban on anime doesn't seem so bad at first, until Saiko reveals that this applies to anime characters, too. Real, living people, not just body pillows and DVDs. That fact causes SMG4, who had been part of the A.S.S and promised Peach he'd go along with the ban, to quit out of disgust. The implications are horrifying, to say the least, and turns the context of the anime ban from a simple overreaction into something much worse; Peach enforcing institutionalized racism against an entire race. The mass burning of anime ''really'' doesn't help her case.
- Meggy getting kidnapped in "The Splatfest Incident" is decidedly not Played for Laughs. Everyone gets panicked when they can't find her at first, which only worsens once they visit her apartment and find it trashed, with claw marks and squid ink everywhere.
- It only gets worse when Desti (who actually wants to help find Meggy) accuses the group's new friend, Axol, of the kidnapping. Everyone starts arguing and fabricating theories, escalating into a full-on civil war inside the apartment.
- Worse, there's sufficient evidence to suggest he did kidnap Meggy - the claw marks, ink, Naruto anime and the fact he holds a grudge against Inklings due to their bullying of him when he was younger. Look at the situation from the characters' point of view - the possibility that the generally nice, friendly manga artist who helped save your close friend from permanent deportation could well be responsible for the abduction of another friend is gut-wrenching, especially for Fishy Boopkins.
- The final scene is Meggy chained up, reacting to her unseen kidnapper... and the door closes on her. Nothing Is Scarier indeed. It doesn't help that dramatic sound effects play in the outro instead of the usual Super Mario Land remix.
- Even worse still is the fact that similarly to the Waluigi Arc, the banner on the channel has changed to something creepy: Meggys face is torn out like paper, leaving an empty white void◊. Somebody must hold a grudge against her...
- Oh, it gets so much worse in "The Inkling Disappearances."
- The opening scene is just Axol hanging his head and then staring directly at the camera. It's quite creepy.
- It's revealed that since Meggy disappeared, almost every other Inkling in Inkopolis has been kidnapped. Inkopolis is now a ghost town and everything is boarded up.
- The Inklings that have been kidnapped are held in these weird orange tubes, unmoving, with pained faces. Meggy's expression says it all.
- The final reveal is of Axol, who has been kidnapped as well! Just... who the hell is doing this? And more importantly, why?!
- The fact that the enhanced anime replicas are involved in whatever's going on suggests that whoever's behind Axol and the Inklings' kidnapping has taken control of the Ink Weaver for themselves...or that the replicas have become sentient and this is all part of their rebellion against their former master.
- Or worse it could imply that despite being a victim, Axol's hands aren't exactly clean, it's possible he's was being forced to draw these mooks (being skilled with the Ink Weaver) by the true mastermind.
- The thumbnail also deserves special mention. Those freaking eyes, man...
- But Wait, There's More! "Mario and the Experiment" reveals the intentions of the Big Bad. Using Axol's pen, Francis plans to use the ink of every Inkling (and possibly Octolings because of Desti) to keep it constantly powerful enough to draw as many waifus as he wants. Such an act would actually kill Inklings! Anyone having Octo Expansion flashbacks yet?
- Francis's method of making Meggy comply: drawing Mewtwo and force-choking Axol. Definitely not played for laughs.
- The ending. We see Axol and Desti watching Meggy helplessly fall into the Ink Zuccer 2000. And then the cheery music plays as the episode ends.
- The Ink Zuccer 2000 is finally activated in "World War Mario", and it's horrifying. Meggy essentially undergoes Cold-Blooded Torture as the ink is sucked out of her, and she's screaming in pain the entire time. And Desti and Axol are Forced to Watch.
- The end of "World War Mario", where Desti is stabbed through the chest by Sephiroth in a sneak attack. Everyone goes silent and stares in horror, before Meggy screams a Big NO and Francis lets out a borderline psychotic laugh. Sephiroth pulls his sword out of her, and Desti weakly lets out her last words before collapsing with a straight cut to completely silent credits.
- Upon being defeated in "Final Hours," Saiko places Francis in one of the zuccer machines and causes him to scream in agonizing pain by activating it. While he deserved it for his actions in the remainder of the episodes' arc, it is still horrifying. Saiko herself even closes her eyes while walking away as though telling herself, "I never wanted this."Saiko: Jackass.
- Peach turning into this... thing at the end of "Mario Does the Chores". Though the horror factor is somewhat diminished by the out-of-nowhere masculine roar followed by "I'm gonna kick your ass, son!" and Mario's reaction.
- In "Stupid Mario Maker 2", Mario accidentally turns an ordinary Toad into a unsettling mishmash of items and creatures. Not helping is the Toad himself screaming "WHAT AM I" and running off in horror.
- Meggy's Roaring Rampage of Revenge after Mario accidentally destroys her treehouse in "There's Something Up With Meggy". And that's one of the least crazy things she does in the episode.
- And to say nothing of the title card...it looks like shes possessed by a demon!
- The Minecraft Plague's titular plague is essentially a goofier version of the Medusa Bug. Any living thing afflicted by it that isn't native to the Minecraft setting is effectively petrified, and while they're still able to talk, they're completely unable to move and still conscious.
Nightmare Fuel / SMG4's Mario Bloopers