Goku May or may not be able to hurt Bill, though I'm pretty sure he can, and non-corporeality is only pre-Weirdmageddon. But even with certainty that Goku can...
>Goku gets the first hit.
>Goku severely damages whatever part of Bill he hits
>Goku doesn't cause enough substantial damage due to Bill's size and Bill regenerates
>Bill is pissed
>Bill turns Goku into Gompers the goat
And that's giving Goku the first hit.
Small tangent from Cal
Seriously though, Bill doesn't underestimate people as much as we make believe. Through 90% of Gravity Falls, Bill could rarely even touch anyone, and even then used hax on people. Only times he could were in Stanley's mind (the first time), where he was fighting '
kids' and was still just testing them, and when he was in Dipper's body and was powerless. During Weirdmageddon, Bill all but won, so he could afford to screw around. He also knew the power of everyone in Gravity Falls. They were literally less than nothing to him in power. He didn't screw around when he blew apart
the one person he viewed as some sort of threat. Heck, he probably used hax more times than not in Weirdmageddon. The times I can remember when he didn't was against the Shacktron, which was immune to
anything Bill could do, hax or otherwise. If you're going to say "but Bill still attempted to punch the Shacktron!", it's pretty clear Bill was humoring the resistance until sh*t got real. And of course, there's his chase with Dipper and Mabel. Even here, it's not as much PIS as we claim, because once again, they're
kids. Kids that Bill wanted alive at that. Remember that Bill needed the kids as they were for leverage with Stanford. And Bill was still opposed by people who he knew could irritate him at best, and used up all their options for victory unless Bill made himself vulnerable (which Bill had to do anyway to rule the universe).
Bill's nowhere near as much of a jobber as we make him out to be. I probably sound like a hypocrite though, from past threads. The masses blinded me.