Dynasty Warriors 6

No i dont recall any but i think xiahou dun and guan yu have the same moves

Sorry about my last answer, I was wrong about there not being any. There are a few, like Yuan Shao and Sun Quan or Cao Ren and Lu Meng, but I still know that Xiahou Dun and Guan Yu are competley different. And you were right about Diao Chan and Zhen Ji, I've heard that they're the same. By the way, for a character to have a cloned fighting style they must use the same type of weapon, more proof of Dun and Yu's differences.

Diao Chan and Zhen Ji - A Whiplike Weapon
Pang Tong and Zhang Jiao - Staff (Only difference is the Elemeny with Pang being Wind and Zhang being fire)
Yuan Shao, Sun Quan and Cao Pi - Short Swords
Sun Shang Xiang and Yue Ying - Bow & Arrow
Zhou Tai, Huang Zhong and Xiahou Yuan - Large Swords
Wei Yan, Xu Chu, Huang Gai and Dong Zhou - All Maces
Xu Huang, Cao Ren, Ling Tong, Lu Meng, Taishi Ci - Pikes
Guan Ping, Ma Chao, Zhang He, Sun Ce. - Spears

Each Character, however, has a different base element (IE: Fire, Earth, Ice, ect.)
Characters which have been dropped: Meng Huo, Zhu Rong, Jaing Wei, Zou Ci, Xing Cai, Da Xaio and Pang De.

This version is just awful...

Jonathan, some of yours are wrong...

Diao Chan, Zhen Ji - Whip
Pang Tong, Zhang Jiao - Staff
Yuan Shao, Sun Quan, Cao Pi - Sword
Sun Shang Xiang, Yue Ying - Bow & Arrow
Zhou Tai, Huang Zhong, Xiahou Yuan - Big Swords(Except for Zhou Tai, he has same moveset, but thinner sword)
Wei Yan, Xu Zhu, Huang Gai, Dong Zhou - Big Clubs
Xu Huang, Cao Ren, Ling Tong, Lu Meng, Guan Ping - Mostly Halberds
Ma Chao, Zhang He, Sun Ce, Taishi Ci - Spears