Many times, most often not permanent, often though shooting themself. "Pebble and the Penguin" uses the "toaster in bathtub" variant. The original "It" review also ends in a suicide.
In the Frosted Flakes section of "Battle of the Commercials." A child freezes in the Campbell's section of "Rise of the Commercials" but may not be dead.
Not sure if this goes here but in one of the videos during the AVGN vs NC saga, in an arguement after the Critic has been kicked into a pile of boxes, the critic calls the nerd a "cow humping transv******". Even though the Nerd is not trans.
"Grandma Got Run Over By a Reindeer" has very rapid red/green flashing from 25:03 to 25:11 (right after Critic grabs Tamara's shoulder). There is a warning at the start of the episode.
Some episodes refer to NC as a woman / not a real man ("Mad Max," "Old Vs New Cinderella"). The "Jupiter Ascending" sketch also debates whether a man or woman should play one of the Wachowski sisters (at the time, only one was out as trans); she is not misgendered but the debate may still be uncomfortable.
Prominent in Hyper Fangirl episodes (biggest examples: Old vs New Spider-Man, Princess Diaries 2, and Christmas Story 2; alluded to in Phantom of the Opera, Chipwrecked, Doom, and all Hyper Fangirl vlogs)
The end of "Phantom of the Opera" reveals Hyper Fangirl was pursuing Critic while in a relationship; however Critic did not requite this affection and her relationship remains fine.
Several episodes have explosions as part of gags. "We Wish You a Turtle Christmas" shows an explosion of nuclear levels and its aftermath for the whole episode.
Jokes about the subject are thrown around. The "Spooning with Spoony" crossover has offscreen rape. There are implications of sexual assault in the Hyper Fangirl arc.
A joke about a doll commercial referencing how weird it was for the family to tell granny their young daughter had twins was, with the grandmother descending into histrionics in the background happens in one Commercial special.