The River Undercuts the Bank is a sword form.
The River Undercuts the Bank is a movement involving dropping to one knee in order to make a horizontal cut at the enemy's abdomen or legs. It is a dangerous tactic without the proper setup.
While Turak Aladon was still retreating from The Boar Rushes Down the Mountain, Rand al'Thor used The River Undercuts the Bank to kill the Seanchan High Lord. During the duel between Rand al'Thor and Be'lal, the Forsaken used this form and almost beheaded the Dragon Reborn.