Nightmare Fuel: Super Mario Bros. Z

Super Mario Bros. Z manages to combine Mario, Sonic, and Dragon Ball Z together into one awesome series. It's got cool as hell moments, hilarity abound, it's share of "aww" moments, and scenes that make you wanna cry. Just like with every series that's got it all however, it's rife with it's own dark times. Given that it's a crossover series of other series that already do a good job of giving you the creeps this was bound to happen, but it manages to stand out from those series anyways.
    The Original Run 
  • Turbo Mecha Sonic. Massive spoilers ahead. For one he's Metal Sonic combined with other Sonic robots. Not long after he forms, he destroys the Death Egg (Eggman's moon-sized base of operations for measure) and forces it to crash land into Mobius. The result is life becoming completely unsustainable from the impact and explosion, but wait there's more! The bloody bastard survives everything with no Chaos Emeralds around to help him. Seeing the damage he wrought triggered a thirst for power and a lust for destruction in him, transforming him into the villain of the first season. He's not done proving to the viewers how nightmarish he is, oh no. He sets out to collect all seven Chaos Emeralds and kills all but Sonic and Shadow while he's at it, also turning more than half the planet into a burning wasteland, and nearly kills Sonic himself had Shadow not show up in the nick of time. Of course, he just hightails it out of there chasing after the Chaos Emeralds that Shadow warped away from him, ending up in the Mushroom Kingdom. Finally making it to the Mushroom Kingdom, he wastes no time overkilling a Goomba simply because the poor sod didn't give it to him (and it wasn't like he could have known what it was anyways). The next time he has a major appearance is his infamous fight with Yoshi, almost adding Yoshi to his kill count to get the Chaos Emerald (and says that he would have killed him anyways even if he simply handed the gemstone over). There's Sonic's nightmare sequence of him after the hedgehog's unceremonious asskicking from the Koopa Bros., and when the three way battle between the heroes, the Koopa Bros., and the Axem Rangers X was underway, he shows up and quickly turns the whole thing into a "him v.s. everything else" brawl (and that's after he already knocked out all of the Koopa Bros.). He achieves a semi-perfect form and offs the entire team of Axem Rangers X with no effort. He almost kills Mario afterward and charges up a Death Ball that would have made Frieza proud. Yoshi's Island is history after that, just barely failing to kill everyone else on it thanks to a well-timed Starman giving Mario and Sonic the edge. In the pipe maze he comes knocking at Mario and Sonic's door with a venegance, stomping them into the curb in a rage over losing the Chaos Emeralds he had, and even when he's been severely nerfed by the Minus World's unnatural makeup he still manages to come out on top in the fight. Again, it's sheer luck here that anyone managed to not get killed by him. Wow, look at this lengthy description. Only the worst of the worst deserve it though, and Turbo Mecha Sonic is no exception.
  • Admit it, the scenes where Mecha Sonic murders Sonic's friends and him gazing at the destroyed Yoshi's Island made you cringe.
  • Episode 8 has a lovely scene where the viewer is treated to a closeup of a dying Rouge. Eeeep.
  • Hell, any scene that has to do with the events on Mobius could qualify, since they almost always involve graphic destruction and even more graphic death.
  • The end of Episode 8, made such with that damn Cliffhanger.
  • Minus World is historically referred to by the simple, cold moniker of "World 36" and is revealed to be a pocket dimension from which there is no escape. During an ancient war between the Mushroom Kingdom and the Koopas, it was used as a method of execution by both sides, who would throw their prisoners down the warp pipe to starve to death; their corpses, as well as those of anyone unfortunate enough to stumble inside, litter the ground of the zone.
    The Reboot 
  • Metallix is the new form of Turbo Mecha Sonic as well as his old form's ultimate transformation, and just like the previous interation of him he shows the audience that he hasn't changed one bit in personality or actions. Mark Haynes/Alvin Earthworm also offhandedly states that Yoshi's ensuing fight against him will be even worse for the poor dinosaur.
  • The first annual Smash tournament has been drawn out to its finals, and just as Team Mario and Team Wario are about to have at it a Bulky Bob-omb crashes the fight and blows the entire ring up. Guess whose back? Bowser. Just like in the previous series he gets his shell soundly handed to him but it's not as if he didn't count on it happening. He had a backup plan involving ingesting a Metal 'Shroom, and it turns him into a new form of Koopa. In short order, Mario is quickly shown to be horribly outmatched by him; Bowser's faster than before, more offensive than before, and is impervious to everything Mario can possibly throw at him. Mario is left charred after the grossly one-sided battle and would have been finished by Bowser, but then Luigi comes in to protect Mario knowing full well that he has zero chance of doing that anyways. The Koopa King was stopped only by a very fortunate timing of Sonic and Shadow's capsule landing squarely on top of him, destroying his metal form. We all knew Bowser was a badass but this series turns him into a legitimate terror more like how he was portrayed in a few choice Mario titles.
  • Kamek shows us that he's not the type of person afraid to resort to dirty tricks to gain the upper hand one bit, threatening to permanently transform Princess Peach into a Goomba if Mario doesn't lay down his life. The music that plays when he's at it? "You Idiot" from Undertale. Again, if Sonic hadn't acted as soon as he did, Mario would have been killed by Bowser.