Arcane S2 Act 2 spoilers: when Jayce was tripping out on his way to Victor, i caught this image flash by for a frame or 2. I believe he was transported to a future where victor's actions led to a total corruption of the world or something similar. based on context cues, I think that the people that Victor "touches" eventually degrade over time and turn into these things. I think Jayce made a promise to a future Viktor that he'd stop him no matter what he'd have to do.