asks: When should you kill off a character, and how should it be done? Like if you have an interesting, rich character but that person suddenly kicks the bucket? How do you do it without being cliche? Can it serve as a catalyst?

Just like how each of your characters should serve a purpose in your story, a character's death should also serve a purpose. For example, it can be the final straw for someone to take action, or it could cause a good person to go dark.

When the death happens should coincide with that death's purpose. If it's to change someone's mind about going on a quest, then it should be when the character has already said no, and the reader thinks, "Well, now what?" This could happen earlier, sure, but it would result in less drama and tension.

Character deaths are very common in stories. If you're trying to avoid cliches, you have to first think about what those cliches are. When you read something that makes you roll your eyes, remember that moment. You'll want to avoid doing what that writer did. For me, a cliche sudden death in movies is being hit by a bus. When I see people in the movie arguing and they step off the sidewalk--still arguing--it makes me sigh, "Watch a bus appear out of nowhere." Then sure enough, SPLAT. I saw it coming because so many other movies have done it.

To make the death happen without being so predictable, take the cliche and change it. Maybe instead of a bus, it could be a guy on a bicycle carrying a long metal pipe he salvaged from somewhere. It's morbid, but think about different ways you can die. All the things that could crush you, impale you, suffocate you, or snap your neck. Pick one that you don't see often. I'll provide some examples of how you can change cliches:

CLICHE: Walking down the sidewalk and being smashed by a dislodged air conditioner unit.

ALTERED: Walking down the sidewalk and being smashed by a meteor.

CLICHE: A parent dying of cancer.

ALTERED: A parent dying of ALS.

CLICHE: The vampire falls and is impaled on a fence/metal rod.

ALTERED: The vampire falls and is impaled by a statue of his ancestors.

makes an excellent point:

I was rolling my eyes when Jynn Erso's father died in Rogue One. At first, I thought it was because I had gotten tired of the trope where the close friend/relative dies in the MC's arms and they are like "noooo!!". But the same thing happened in Coco and I was almost crying during that scene. So I think the issue with Rogue One was that I didn't care enough about Jynn or her father to care that he was dying. So my advice is that you MUST make the reader care about your character before you kill them--and if you don't want your reader to care about the person who is about to die, make your MC sympathetic and have them care when that person dies. The reader HAS to care when something as big as death happens in a novel, one way or another. They could be cheering on the death, as long as it's intended, that's a fine response to a villain's death. The worst thing they could feel is indifference.