Your character cannot get decapitated in-game though there is a costume that, according to the Wiki "Makes your survivor appear as if they are headless."
(A major theme in the written notes, spoilers, I'm not sure how to explain without them)
Characters often talk about their purpose in life, especially after they find out they are clones. They discuss if their memories are real, and if their choices really are their own.
Characters write about this in their notes a lot, including this quote from Helena "I'm starting to come to terms with everything myself. Even if my memories are someone else's or aren't real to begin with, what I've done since I arrived on these stations was my choice. What I do from now on is my choice. That's who Helena Walker is."
They end up unexpectedly in the setting of the story and discuss their purpose there.
One character was brought back to life, given fake memories, and doesn't know that he died and finds out throughout the story.
Another has to deal with having the memories of two different people.
Many characters sacrifice themselves or put themselves in a dangerous situation to save others in the written story. One does in the end of Genesis 2.
Technically the player could sacrifice themselves or a tamed creature to save themselves/someone else, though it is not necessary.
sort of? they aren't a main part of the game, there's a costume called "Strawman Costume"
In Genesis there are robotic humanoids called "Corrupted Avatars" that you fight. (a more important part of the game)
In the written notes you can find in the game, the main villain often lies to and manipulates characters, pretending to be a "kindly, curious old man" in later parts of the story
Especially to one of the protagonists who thought of him as a friend.
No teeth are damaged, but some items you can collect from dinosaurs/creatures that have died are their teeth. (It is not graphic, just an image of a dinosaur/creature tooth)
Dinosaurs and people bleed, however it's not excessive. However, in Genesis 2 the main villain takes over a spaceship with horrific body horror you travel through a biome made of his own flesh, and you can see his organs.
Ghosts are not a regular part of the game, but there are ghost creatures that can appear during "Fear Evolved" events, and costumes that can make certain tamed creatures look like ghosts, that you can use any time if you have them.
While not as an intentional suicide scene, in Aberration's notes, the character Skye walks off of a cliff thinking that she is dreaming and that it would wake her.
A lot of characters' stories have sad endings, the ending of Genesis Part 2 could be considered sad. There are sad moments but there are hopeful ones as well.