The souls that Lith had summoned didn't belong to long-dead people like usual. They were the spirits of those that Xedros had sacrificed to turn himself into a Dragon. They didn't get to possess any corpse but their own.
It boosted their strength and fury beyond what Lith had ever accomplished before. As the darkness that animated the souls eroded the bodies, it also empowered them, restoring a part of their original powers.
At that moment, despite being covered in wounds, Scarlett found the strength to curse at Lith via their mind link that she had never broken.
'What have you done? You don't produce undead, but lesser Abominations. Without a body, no healing can bring Sedra back!'
'I didn't do anything. The souls acted of their own will. Besides, do you really think I could conjure the Demons of Darkness from someone alive? You've seen the Hydra shade. The body may still be here, but Sedra was already dead before our arrival.' Lith replied.