Because his life hasn't been entirely too settled by far of late, Eight is going to end up being Zagreus, which means he's going to more-or-less end up being an eldritch abomination. Appearance-wise, he's going to look exactly like he always does, but pretty much the rest of his demeanor is going to be as un-Doctorly as you can get, although he depending on how things go he might have brief moments of being the Doctor.

Additionally, his voice is going to come with a nifty sort of reverb effect just underneath it, which will get more noticeable the angrier/more annoyed he gets.