Here’s some I know:

• Dolphins rape other dolphins
• Praying mantis females often eat the head of males they have sex with. Some spiders do that too.
• Mass extinctions have occurred in the past, way before humans existed
• 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)