It was a close call.
Lucifer, who had been kicked back into Juin's Soul Dimension, heard his call for merge in time and quickly took over his body. However, having been taken over by Hades' consciousness and forced to expend a huge amount of soul power, however short that was, Juin's body was completely devoid of energy.
It was already a miracle that he could even find the energy to flail around earlier.
Using the last remaining strength in Juin's body, Lucifer called upon a small spell to break his fall. Fortunately, he managed to draw the diagram needed for the spell before Juin's body hit the ground.
Unfortunately, he was unable to draw the best spell he could given the lack of time. Hence, he only called upon an easy spell, which broke his fall partially by creating a thick bed of flames.