Defeat Li Dian and Yue Jin before they re-gather their troops. Defeat either Cao Xiu or Zhang Liao after they appear. Achieve 140 KO Count. This on Expert mode. Li Dian and Yue Jin will start to re-gather their troops approximately 2 minutes into the stage. If you defeat them before 2 minutes, a Precious Item Report will appear. Try to accumulate as much KO Count as possible during the period of time before Cao Xiu and Zhang Liao appears. Defeating one of the latter 2 enemy generals will give you an "S" rank. I recommend defeating Cao Xiu, because he's a lot easier to defeat than Zhang Liao. Just a mention, to clear the stage you need to defeat the correct enemy entry point captain to find the route of retreat. The correct one is said to be random, but of the 8 times I played, the exit had always been the bottom entry point. So maybe that is the one?
Get 800 kills in Hard Mode
On hard mode get 50 kills in 4 minutes
Get 100 kills in 3 minutes on hard mode
Achieve 300 KO Count in under 4 minutes on hard.
Get 100 kills in 6 minutes and 35 seconds on hard mode
Get 300 KO Count in under five minutes and win with the difficulty on hard
Achieve 100 KO Count in under 4:30 minutes on hard.
Don't let any one pass the bridge and kill all generals on hard
Kill Cao Ren, Zhang He, Xu Zhu and Xu Huang on hard mode
On hard mode, get 400 KO Count before Xiahou Duns reinforcements comes
Before your ally troops get eliminated, defeat Guan Xing and stop the rock attack on hard
Beat Hua Xin, Hua Xiong and Lu Bu in under five minutes on hard