Find the decorated wooden box containing Liu Chan in under 2 minutes.
Defeat all enemy generals.
Achieve 200 KO Count.
Zhao Yun and Liu Bei both reach the bottom right Chang Ban Bridge all in under 13 minutes 30 seconds.
I strongly suggest playing the game at least once before trying for the weapon, mostly to get an idea of where the decorated wooden boxes appear in the castle. Even though which decorated wooden box contains Liu Chan is random, where the decorated wooden boxes appear in the castle are always the same. So knowing their locations beforehand will help in your search for Liu Chan. Because the 2 minute time limit is not plenty of time. Saving the game after finding Liu Chan is also recommended.
Defeat Cao Ren and Xu Huang to open the North castle gate. Defeat Xu Zhu, Xiahou Dun, Xiahou Yuan, Yu Jin, and Yue Jin to make Liu Bei start retreating from the battlefield. It is acceptable if Xu Zhu, Xiahou Dun, Xiahou Yuan, Yu Jin, and Yue Jin are defeated by allies and not by the player. Do this on Expert mode
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