All fourth weapons must be completed on Hard or Chaos mode:

Cao Cao Battle of Xia Pi, Wei Side: Defeat Gao Shun before you get the message that he's guarding the dam then defeat.

Da Qiao Xia Kou, Wu forces: Defeat Cai Mao and Gan Ning before Ling Tong is defeat.

Dian Wei Wan Castle, Cao Cao side: Meet with Cao Cao, Take him to escape gates, Don't let no one get past you until u get the message that Cao cao escaped.

Ling Tong Hei Fei, Wu forces: Defeat Zhang Liao each time he appears.

Lu Bu Battle of Chang Shan kill 1000 enemy troops.

Zhang Liao.

Zhang Liao Hei Fei, Wei forces: Freely kill many generals and sub-generals till 3 messages apprear with Wu soldiers admiring Zhang Liao.

Zuo Ci Hu Lao Gate, Allied forces: Kill Lu Bu on hard mode.