So in this article, Chris Sutherland said "We've always been fans of Shovel Knight,and thought it'd be great to have some guest star characters from the rest of the indie community. It's great for indies to be able to do that. There's no kind of big barrier, you don't have to go through seven levels of approval, you just go: yeah, we're going to do that."
Makes me wonder if there will be any other indie game characters... Shantae, maybe? ...Is it wrong that I want Sans from Undertale in this game? Or more guest characters at all? I'm fine with Shovel Knight, though.