Instructions
Equip yourself with the crossbow from your available weapons.
Shoot at the mountain lion as it charges you, then sidestep it as it jumps toward you.
Shoot the mountain lion repeatedly if it misses you. If it lands on top of you, rapidly tap the "ZCB" button to push it off, then shoot the lion once you knock it off. Repeat these steps until the mountain lion is dead. It should take four shots from the crossbow to kill it.