This is unlocked by unlocking the character Huang Zhong.
You can unlock him by completing Target 1 on Wei's side of Mt. Ding Jun.
This target requires Huang Zhong to be defeated and for Xiahou Yuan to survive. Just make sure you defend Xiahou Yuan when they get into a fight because Huang Zhong will be a bit beefed up.
Upon completing the level and unlocking Huang Zhong, this will unlock.