Here’s some I know:

• Dolphins rape other dolphins https://theconversation.com/dolphin-sexual-politics-gets-the-tabloid-treatment-6063
• Praying mantis females often eat the head of males they have sex with. Some spiders do that too, like the appropriately named black widow spider. https://en.m.wikipedia.org/wiki/Sexual_cannibalism
• Mass extinctions have occurred in the past, way before humans existed https://en.m.wikipedia.org/wiki/List_of_extinction_events
• Genetic mutations often lead to inviable offspring or awful conditions (I don’t know specific examples off the top of my head)
• Parasites can take control of insects and lead them to drown (also don’t know examples off the top of my head)