Vernon figured it would be best to kill the trio quickly, as to not let them get the better of him. His initial plan is to electrocute them, but he realized that there were no electric things to throw in nearby. Electric power was rare, especially in the savage lands, though some magical artifacts had similar electric effects. Luckily enough, Vernon remembered spotting a staff hanging on a mantle in the hall. He'd completely ignored it before since he had no magical ability and thus wouldn't be able to wield it. To kill the girls in the spring though, he'd only need to toss it in. He retreated back to go find it.
With a faint touch to the tip, he felt static. The staff was definitely electric. He hurried back to the springs, but unfortunately for him, the winged demon had already left the spring, drying off with her towel from a slight distance, so it was highly unlikely she'd be going back in. "Oh well," he thought. At least he could pick off two of them before finishing the third. He dashed in, just close enough to throw the staff.
The two demon girls never saw it coming, only reacting after the "plop" of the staff into the water, still more confused than afraid, but their eyes widened as electricity began to surge through their bodies. Of course the convulsed, rippling the water. They reached for each other, clasping together for some sort of comfort in their painful final moments. One began foaming at the mouth. In the end, after their short struggles, one lay draped over the side of the spring, most likely aiming for escape from her fate, while the other simply floated face-first in the water.
The duo didn't die quietly, letting out a few shrill screams of anguish, and obviously attracted the attention of their winged friend. Vern hoped she'd be stupid enough to end up electrocuting herself too in her investigation, but he was not that lucky. She saw the staff and steered clear of it and she actually turned out smart enough to quickly identify Vernon before he could get out of sight. She flew up into the air and confronted him, not intimidated at all.
"You may have got the others with a cheap trick, but if you're gonna fight me, I'll rip your insides out," she said.
"I'm armed and you aren't," Vernon said, brandishing his sword. "If you don't want to end up like your hot tub buddies, you should apologize and surrender."
"I'm armed with all I need!" she retorted, brandishing her clawed hands with a cocky grin. The winged demon shed no tears over her dead comrades, instead appearing excited.
Vernon weighed his options quickly. She had a point. Some demons' natural claws such as hers were considered very strong weapons on their own right. They were strong enough to block and deflect sword swings in the hands of a talented demon and could tear through flesh like butter. With her wings, she also had the high ground. One option he considered was crippling her wings or cutting them clean off to disable that advantage, or even to flat out ditch the sword and grab her down by the legs if he could manage to reach the very moment she swooped down, but by then he'd probably already be being disemboweled.
(Next time Vern's gonna need some proper battle strategy! I actually agree with him starting to treat the imp better. Maybe they can even eventually form mutual trust eventually, but that'd be way down the line far after the events of this story, so I won't get ahead of myself I suppose)