In book 2, when Wei Wuxian is conducting Empathy with Nie Minjue's Spirit (end of the book, chapter called "The Beguiling Boy") a character's fans and paintings are burned. These objects are extremely important to him and it is upsetting to read.
The main character seems to suffer from alcoholism, but the effects of that aren't explored, and it is more so portrayed as a character quirk than a disorder.
There are many ghosts. The main character is a ghost cultivator, so there are many ghosts, walking corpses, living corpses, fierce corpses, and paper effigies.
Both main characters are autistic coded. As an autistic person, I really love the representation and think that Wei Wuxian and Lan Wangi are great autistic rep. (also Wen Ning and Nie Huaisang!)
Not specifically stated, but the main character’s new body was acquired through a suicidal ritual, and the main character dies offscreen by ordering corpses to kill him, neither are thoroughly mentioned)
A character gets trapped in the walls of a mountain in which the walls have corpses embedded everywhere. It’s brief but does discuss asphyxiation (spoiler alert he’s okay)
In the beginning past abuse and its effect on a character said to be mentally ill is mentioned. A character is treated and spoken of very poorly for supposed mental illness. At points, the protagonist "acts crazy" to disguise himself. - i.e everything Mo Xuanyu related.
Several explicit scenes, but they are optional as they are not technically necessary to the story, taking place at the end of volume 4 as a kind of after credit scene, except one at the beginning of volume 4 in the bathtub which is plot relevant