Here is my bet. He had writers come up with a few "zingers". Biden has been searing them into his (all too questionable) memory. Wallace will set them up. The press will play them in a loop, and that is all they will talk about as the MSM declares him the greatest debater since Lincoln.
The "zingers" will, of course be highly contrived and obvious, but that won't matter, even if Biden steps on his own lines.