The spider-eating guy

[BendyBread]

There is an illustration of Wilbur together with a dog in the intro of Black Plague when you start a new game. He looks like a wolfman, his mouth seems deformed to look like that of the infected and is wearing some kind of miner's helmet. That kind of mostly solves the mystery.

PLEASE say you're kidding.

That's Red.

There's no answer to whether that's Red or Frisk. The narrator mentions Red when the image appears, but it's also possible that it's Frisk, since he tore up some dogs.

You would think that when they mention Red and show a picture, it'd be a very clear indication that it was indeed him.
I don't remember if he ever ate dogs or not, but that could possibly be part of the picture. Lastly, Red is wearing the workers suit. I havent played black plague so I'm unsure if Frisk also wears it.