An early episode has a decently long discussion about dogs with knives attached to them killing each other, and while nothing is confirmed or occurs on screen, a planet full of aggressive knife dogs does exist in the canon and it can be assumed that a lot of death occured
Several times; David is ordered not to breathe and complies (episode 10), David is strangled by Trexel at one point (episode 16), Trexel is put in a small cage and struggles to breathe before being let out (episode 45).
In episode 1 David is put through clone "education" which involved a lot of drilling and sparking noises and sounded very painful, and in episode 40 Hartro creates a "gauntlet" of challenges for David and Trexel which involve being burned, tormented by disembodied voices, and a buzzsaw.
As of season three, every episode starts with a brief kidnapping, and often ends with vague planning of another kidnapping. This all has the same level of vaguely upsetting levity as the rest of the show
There is discussion over whether a client is two people who share a body, in which there are offhanded comments that could be interpreted as ableist against DID (episode has content warnings of ableism)