during the battle of Xia Pi, Wei Side, you must defeat Gao Shun before you get the message that he's guarding the dam then defeat Zhang Liao.

Wu Zhang Plains, Wei Forces; Kill any three officers, Zhuge Liang dies, Destroy all arbalests when they appear

Flee from Chi Bi, Wei Forces. Defeat all the enemy reinforements and defeat Sun Quan last.

At Wan Castle, Cao Cao side, you must meet with Cao Cao, help him escape the gates, but don't let no one get past you until u get the message that Cao cao escaped.

At the battle of Xia Pi, Lu Bu's Forces, yuou must defeat all of the generals and subgenerals before Cao Cao arrives. Remember, do not let any of your own generals from dying.

At the Liang Province, Dong Zhuo's Forces, you must take all 5 bases and defeat Ma Chao and Pang De.

At the Battle of Xia Kou, Huang Zu's Forces, you must beat Ling Cao and Ling Tong within 2 minutes of the stage.

At the Escape from Chi Bi, Shu's Forces, you must defeat all enemy generals and sub generals.

At the battle of Fan Castle, Shu Forces, you must beat Niu Jin and Yue Jin before the water attack is triggered.

At the Yellow Turban Rebellion, Han Forces, you must kill all subgenerals and officers outside of Zhang Jiao's fort.

At the battle of Mt. Ding Jun, Shu Forces, you must beat Xiahou Yuan and Zhang He within 5 minutes before Cao Cao appears.

By clearing musou modes, you unlock other characters. Some will be unlocked by beating a set number of musou modes in a faction.

Shu Faction
Zhuge Liang - Any Shu officer musou clear.
Jiang Wei - Two Shu officers cleared.
Pang Tong - Three Shu officers cleared.
Liu Bei - Four Shu officers cleared.
Guan Ping - Guan Yu's Musou Clear (Battle of Fan Castle)
Yue Ying - Zhuge Liang's Musou Clear (Battle of Wu Zhang Plains)
Wei Yan - Huang Zhong's Musou Clear (Battle of Bai Di Castle)

Wei Faction
Sima Yi - Any Wei officer musou clear.
Xu Huang - 2 Wei officers musou clears.
Zhang He - 3 Wei officers clears.
Cao Cao - 4 Wei officers clears.
Cao Ren - Cao Pi's musou clear (Battle of Wu Zhang Plains)
Xiahou Yuan - Xiahou Dun's Musou Clear (Battle of Fan Castle)
Pang De - Ma Chao's Musou Clear (Battle of Bai Di Castle)

Wu Faction
Zhou Tai - Any Wu officer clear.
Lu Meng - 2 Wu officer clears.
Huang Gai - 3 Wu officer clears.
Sun Jian - 4 Wu officers clears.
Sun Ce - Sun Quan's Musou Clear (Battle of Bai Di Castle)
Da Qiao - Sun Ce's Musou Clear (Battle of Xia Kou)
Xiao Qiao - Zhou Yu's Musou Clear (Battle of Chi Bi)
Gan Ning - Ling Tong's Musou Clear (Battle of Yi Ling)

Neutral Faction
Lu Bu - Clear musou with one officer from each faction (except neutral).
Diao Chan - Lu Bu's Musou Clear (Battle of Xia Pi)
Dong Zhuo - Diao Chan's Musou Clear (Battle of Xia Pi)
Yuan Shao - Cao Cao's Musou Clear (Battle of Wu Zhang Plains)
Zhang Jiao - Sun Jian, Liu Bei, and Cao Cao musou cleared.
Meng Huo - Zhuge Liang and Lu Xun musou cleared.
Zhu Rong - Meng Huo's Musou Clear (The Nanman Campaign)
Zuo Ci - Guan Yu, Zhuge Liang, Ma Chao, Huang Zhong, Liu Bei, Sun Quan, Sun Ce, Zhou Yu, Sun Jian, Ling Tong, Lu Xun, Lu Bu, Diao Chan, Meng Huo, Xiahou Dun, Cao Pi, Cao Cao, and two other Wei officers (your choice -- cannot repeat previous guys).