The final boss seems impossible to beat. Even if you don't get lumped with the support enemies who constantly revive, as soon as the Dark Knight gets one hit in the battle is over.
The build speed upgrades don't seem to make much of a difference at all. I didn't upgrade til I was at 80% on my second go and I still managed to finish at Wave 25 or thereabouts.
 "Sentry Knight Conquest"){kind=icon}
 "Egg Knight"){kind=icon}
 "Dead Rampage"){kind=icon}
 "DungeonUp"){kind=icon}