Don't know whether this has been posted already, but this is a suggestion for everybody out there who can't kill Stephan in the Sky Fortress fast enough that his Earthquakes don't appear.
I have noticed an interesting "feature" of this earthquakes: if you die and resurrect but don't move at all, you become immune to the earthquakes.
In other words, what I do is, once it is announced that the earthquakes will happen ("... Ground-Shaking shenanigans thing"), I carry Stephan to one corner where I think those ranged zombies won't see me (their arrow shower will most likely push you), die once for the earthquake, resurrect using one token, then proceed to kill Stephan.
Yeah... you still die once, but I found this more reliable than running around with zombies, Stephan and earthquakes chasing after me.
Edited by Asmrow, 26 June 2018 - 04:54 PM.