Who are the enemies of the mountain lion?

A mountain lions only enemy is any animal that has the nerve to try to attack it. Its very rare that the mountain lion gets attacked, and even rarer if the mountain lion loses the battle.

A Mama bear with cubs will kill a cougar. but this is a rare incident indeed.
Humans are a mountain lion's main threat. Humans are responsible for their loss of habitat, habitat fragmentation, and being hunted by people. Other than that, nothing preys upon this animal.