“I read a story in a western magazine with photos about a mule which killed a mountain lion.”
Obviously, the mountain lion was kicked to death. The herbivore killed the carnivore. It is usually the opposite. The meat eaters prey on the grazing and vegetarian animals. These videos are all over YouTube.
Snopes says not true so I figure it is true.
See the photos. https://www.snopes.com/fact-check/mule-vs-mountain-lion/
Look What Happened When This Leopard Attacked Donkey
https://www.youtube.com/watch?v=XJRy-IGaqcA