- Sure, the whole story can be seen as this, but shit really hits the fan in the Osaka arc. From the outbreak of the demons to the sick freaks that make up the Osaka team, it's hard not to be afraid.
- The Italy arc— The fact that hundreds of Gantz teams are getting killed from the demonic statue aliens really dials up the nightmarish scenarios seen in this arc.
- The Dinosaur arc is no slouch in this department either. Behold, the triceratops alien.
- Which leads to how the Dinosaur Arc kicked off in the first place. Shion Izumi paints blackface and starts shooting up the crowd in Chapter 123. All just to return to the game. Definitely a Trauma Button for those who suffered from urban violence.
- Apart from facing "fairly normal" horrific monsters time to time, there is the Nura alien, Nightmare incarnate. Also, don't forget the upcoming apocalypse... in a week. The apocalypse does not disappoint in this department (see below).
- The king of all nightmarish arcs, though, is the Catastrophe arc. As if the humans weren't in a bad enough shape already...
- And just when you think it couldn't get any worse, IT DOES. The virus affecting Gantz causes him to create pixelated monsters that explode when they die. Read chapter 342 at your own risk.
- Chapter 347 is nothing but pure Nightmare Fuel. If a light spore touches a person, body parts and faces will literally burst from the said person's head and become THIS ABOMINATION. Yeesh...
- One of the most horrifying elements is what the giants do with the humans they capture, with atrocities ranging from recreationally hunting them with their kids and feeding human giblets to their pets, to processing them in a mass-slaughter factory and casually snacking on them live (which fittingly triggers and justifies Sakurai's transformation From Nobody to Nightmare).
- The giant aliens have a tool that can "upload" a human's visual data from someone's mind and use it to track the person in question. Already Paranoia Fuel on its own, it's described in a deadpan tone by the aliens as not government or police equipment, but a children's toy. Let that sink in for a moment.
- The brief shot in the anime Title Sequence of Keinote holding a Gantz gun to her own head. While smiling.
- The Oni Arc features a scene with a shapeshifting alien that enters the ear of a Red Shirt while transformed into a fly, it then moves to inside his torso and turns into a elephant.
Nightmare Fuel / Gantz