With the blade still embedded in her shoulder, he pulled it downward as he dropped below the sweep of her blade, letting it pass harmlessly above his head. At the least, the downward motion of his blade would likely sever nearly every tendon in the shoulder, leaving only those above the original wound, and make the arm a bonafide liability, rather than simply useless. 

This motion also had the beneficial effect of allowing the incoming fireball to pass harmlessly overhead and detonate somewhere on the mountainside behind him and too far away to make a difference. Planting his left hand in the water surrounding both himself and the young dragoness, Arthur released a second torrent of electrical current and sent it straight to the young woman's heart. The attack held enough current to paralyze the muscle outright, though he also spared some power for the rest of her body in an attempt to render her entirely immobile while she died. There was no telling what kind of damage she might be able to do by flailing about in her final moments.