The third form of the Vanishing Stance was exhausting as the first and second.
To perform the third form, Ned must exert more energy not just from his arms but all over his body.
The first form of the Vanishing Stance was a mastery of its movements. The first form's attack varies from opponent to opponent. But the generic attack was a stab, pull, then slice. Mastering this easy movement will lead to the second form: which was explosiveness. This however took a lot of Ned's energy. Without mana to support his attacks, his energy was drained at a faster rate.
Mastering the explosiveness of the second form will make Ned's attack powerful even without using mana. This made Ned awe-inspired to train the Vanishing Stance since he never knew that energy in the body could be used to make an explosive attack.