The Mandarin Duck Formation was by no means a rigid formation. The treacherous wetlands of Southern China necessitate any military unit to be able to change formation at a moment notice.
Liang Yi Zhen (兩儀陣, lit. 'Two Forms Formation') and Wu Xing Zhen (五行陣, lit. 'Five Elements Formation')
The Liang Yi Zhen split the original Mandarin Duck squad into two independent teams known as Wu Xing Zhen.
Xiao San Cai Zhen (小三才陣, lit. 'Lesser Three Powers Formation')
The Xiao San Cai Zhen reorganised the Liang Yi Zhen into two ranks, with Lang Xian (狼筅) at the centre, pikemen at the left and right side of the Lang Xian, swordsman and Tang Pa (钂鈀) guarded the flanks.
San Cai Zhen (三才陣, lit. 'Three Powers Formation')
San Cai Zhen was deployed in cramped terrain, where original Mandarin Duck Formation could not deploy properly. It was also more flexible and nimble than the Mandarin Duck Formation, suitable for ambush or flanking maneuver.
Other blog posts in my Mandarin Duck Formation series:
Mi Zhan — the original Yuan Yang Zhen
Qi Ji Guang's Yuan Yang Zhen — part 1
Qi Ji Guang's Yuan Yang Zhen — part 2
Qi Ji Guang's Yuan Yang Zhen — part 3
Qi Ji Guang's Yuan Yang Zhen — part 4
Qi Ji Guang's Yuan Yang Zhen — part 5
Qi Ji Guang's Yuan Yang Zhen — part 6
Xu Guang Qi's Yuan Yang Wu