Jayce has seen this before, or a version of it, so when he knows it's about to crank, he tells the other two: "Keep your head down!" When they made Hextech for the first time, it should have killed both of them with how much energy was crackling and zipping in every direction. He is not surprised at all when the Hexcore amps up and that is exactly what happens. He leans down and keeps his head close to Viktor's as he holds onto him and keeps healing through it.

He doesn't look as Viktor begins seizing because he knows he'll panic, and instead all he can do is close his eyes tight and not get blinded by the incredible explosion of energy. That luckily does not actually hit any of them, but zips around the other parts of the lab instead. Jayce never saw the Hexcore in action, but Hextech at least is familiar.

As Viktor drops back, he looks at the incision and sees something changed. He frantically grasps for a pulse, even if he can see Viktor breathing unsteadily, just to reassure himself. "We need to close him up, quickly. Are you okay?" This to Nadine, hoping that she can keep a steady hand after something as insane as what just happened. Otherwise he will have to. His hopeful eyes turn to Alucard. "Can you move the Hexcore, please?" He doesn't trust that he won't immediately smash it after seeing what happened, but getting it away from Viktor is vital right then.