Right. Yes, Dr. Telephosphor should have expected this from someone who had basically asked him to shoot them. Of course, he didn't plan for it and had instead backed himself into a corner with a swordsman in full plate armor who had complete immunity to the exact things he was good at. This had to be the exact definition of an unfair fight.

"That... that makes no sense."

By all rights, he should just follow the gentleman's suggestion and make the quickest egress inhumanly possible, but instead he found himself just standing there and staring.

"You're the Fountain of Youth. That implies that you're immune to aging. Wh-why would you also be immune to disease and toxins?" He asked. His inhuman nature afforded him a curious advantage in this instance: incapable of expressing his emotions in human language, his tone was perfectly even and his face blank. His completely black eyes made it impossible for his opponent to even see where he was looking.

"D-do you realize that those are completely different vectors for illness? Do you even know how aging works?"

He backs further into his corner and pulls out a very, very large grenade, which he immediately activates in his hand.

"I'm not leaving," he says, as thick clouds of harmless water vapor begin pouring out of the device, completely enveloping them both. If one were to look carefully, one could see a set of gills open up on the sides of his neck to breathe it in. "I need your body. For science."

When the vapor clears, the frog-man will be somewhere else entirely.