The dwarf does not appear to be paying attention to what he is doing, Lan Wangji notices, as he takes a step or two to the side to watch him descend. He sees him slip and throws himself forward, using Bichen to yank himself into a speed that would otherwise be impossible.

It is not enough to catch the dwarf completely, but it is, barely, enough. Bichen spears through the back of the dwarf's tunic as he plummets, and then Lan Wangji's hand is on his arm in a hard grip as he slews him sideways into a hard tumble to the ground.