While this manga has its violent moments, Chapter 207 trumps them all by showing Lucifer jamming her hand through Furuichi's chest and ripping his heart out.IN DETAIL.
And as if that wasn't enough, after Lucifer cuts Furuichi's heart (the representation of his soul) into pieces, Takamiya delivers them to his underlings as "desserts"... and they EAT THEM.
Takamiya's first meeting with Lucifer. She killed everyone but his dad when he was a kid, the dad's in a coma, and since he couldn't control her, he didn't leave a tiny dark room in his house for two years until Saotome showed up to help. Keep in mind he looks no older than eight or so in the flashbacks.
Himekawa uses a device to somehow cut the link between Oga and Beel. His absolute panic upon realizing this and looking for Beel is pure Adult Fear.
The following chapter shows Beel's version of said terror as Oga can't see or interact with him and he freaks out. When he comes back with Kanzaki, Oga is pretty much on the verge on death.
The Black Fog that turns people into stone. All over the city. And it seems sentient enough to go after and attack people who are trying to avoid it.
Fuji and Satan. The Six Upstarts AND the entire pillar squad didn't even slow either of them down. In Fuji's case 20 seconds was (rightfully) deemed too long to stall for in a fight against him. And in Satan's case the entirety of the pillar squad was finished in a similar timeframe. And all of them turn to stone.