As with the series it's based on, An Adventure of Mutual Killing has a heaping dose of Nightmare Fuel ready in wait.
UNMARKED SPOILERS AHEAD.
- The executions, of course.
- The first killer, Chiharu Akio, has her face mutilated by a drill and saw. When she discusses her execution as a ghost, she notes that the saw cut into her eye. Yikes.
- The second killer, Rei Ueda, is pulled under murky water by reanimated skeletons, and drowns.
- The third killer, Shinobu Kurosawa, is instantly obliterated by every one of her lethal creations firing at the same time. By the time the execution is over, there's literally nothing left of her.
- The fourth person to be executed, Chiharu (this time in the form of Beta), isn't even a killer. Monokuma just hates her enough to have her disassembled and tipped into an incinerator while still conscious.
- Toyozo's many murder schemes.
That's Sodium hydroxide. Remember your chemistry, Toyozo? That stuff leaves nasty burns.
- His first scheme involved pouring Sodium hydroxide, AKA 'Lye', into the swimming pool while everyone was inside, oblivious to his actions. All the while, he's desperately trying to talk himself out of it.
- At the time of his death, he was planning to murder Katsuo and use buckets to transfer his blood across the school and hide the real scene of the crime.
- Chapter 4's motive. The cookies that Tamaya served the students were laced with a poison that would induce nausea, abdominal pains, vomiting, intense fever, and diarrhea. It is revealed that one of the treats was enough to cause severe symptoms. Sentoki had three.
- Katsuo tried to hypnotize Sentoki to ignore the pain by first focusing her attention on it. As she started writhing about, he hesitated, almost considering leaving her in this state of pure agony.
- Tamaya has to find out that the Bio Lab is a morgue the hard way. She pulled out one of the bodies, which happened to be Chiharu. Just imagine her mutilated and torn up face staring at you. Yikes...