* The Suicide Virus. Yoshimatsu's wonderland gone horribly wrong. Nami can freeze people's blood. Okada's shinigami. The owl. You know what, it's just easier to say everything is nightmare fuel.
* Yura's power is to create bubbles of high-compressed air that explode when he wants them to. He uses it to kill everyone in his way at the slightest provocation.
* Yuta in Chapter 5 creates a barrier with enough oxygen for 4 hours. Nothing seen outside the barrier moves, with the sun and clouds staying in place. It's an isolated world in itself and you're at his mercy.
* Nami's power lets her freeze moisture, including blood. One prick of her ice claws and you'll have spikes of your own blood jutting out of your arm.
* The Promise of Death power, belonging to Okada. Not only will it kill anyone who makes a promise with him (note that he dictates whether or not its a promise, not the victim), barring power-users, he's so petty that he uses it to kill anyone he thinks insults him. They could be well-meaning and he'll still condemn them to death, such as a little girl who was looking for her parents.
* Kanon has the power to make metal explode violently. As bad as that is, she's also AxCrazy and immature, willing to kill for just looking happier than her.