- "Fine." To elaborate, it's what Plutonian says after his first rampage: total destruction of Sky City, the city where he lived. He's done with being a hero, and decided to discard all responsibility. And it's just the first act...
- An alien virus that killed only children, melting the flesh and muscle and animating the skeletons. As if that weren't scary enough, it's sound-based and travels on their screams. Just to be clear: not only the victims' screams, but also the screams of anyone else who sees them. The sound that causes this, which only Plutonian can hear before it's unleashed, is something he describes as beautiful... and as mentioned above, is a component of the screams of children dying in agony. And this is before he went psycho.
- Modeus using Bette Noire's body and enhanced gravity powers to beat Tony to a pulp and then rape him.
- In a bid to protect humanity from the Plutonian's eventual wrath, Hornet made a deal with the Vespa alien race to provide the coordinates for every Earth-like planet his team has ever visited in return for their assistance in neutralizing the Plutonian. Considering there were Earth-like planets with sentient life, his choice condemned countless lives to slaughter.
- Every method used (with varying levels of success) to counter or contain the Plutonian is horrific — wrapping him to the point of mummification inside skin cloned from his own skin, trapping him at the point of heat death of the universe, making him incapable of movement or any action save existing for all eternity, and even killing a third of the population of Earth — and ultimately ending the human race within three generations — simply by the act of releasing the entities capable of stopping the Plutonian. Even the ultimate redemption of the Plutonian comes at tricking him into destroying himself, then siphoning his essence off and sending it throughout the universe in the hope that someone will create something positive with it.
- The very premise itself. The Plutonian started off as a smiling and selfless hero, always ready to do good, fight evil and save the day... but there was always something bubbling under the surface and it takes a series of really awful events to make him feel heroism was no longer worth it. His sheer power and strength makes fighting him futile, and he has no compunctions with who he kills. The populace is shown to be utterly terrified and suicide has become commonplace. To put it another way: Imagine if every nightmare scenario that Lex Luthor and Batman could come up with for if and/or when Superman went supervillain came true. Only, instead of world domination, "Superman" wants to just kill everyone, everywhere. The only reason he hasn't done so already is for the sake of drawing it out.
Nightmare Fuel / Irredeemable