A Wham Episode is all three. "This is the episode meant to radically alter the status quo, and in doing so send a major shock through the viewership."
Well, yeah, I meant the three to be largely a matter of degree.
Homestuck is odd because it has semi-lengthy periods of relative stability that every so often get turned on their head by some new development. I didn't watch Lost, but my impression, both from what I think you're getting at and from outside descriptions, is that it basically had a game-changing twist every episode. Furthermore, the entire point was that we didn't know anything, that we were "lost", so to speak; with Homestuck, it's more like every time we think we do
know everything, Hussie pulls the rug out from under us.