So you think you're hot stuff, eh? You actually did it, you punched out Cthulhu. You drove the Hit Points of that Physical God, Demon, or Eldritch Abomination down to zero, and it vanished.
Unfortunately — he's coming back. You see, what you killed was just part of him. The physical part that was inhabiting our universe at the time. His reappearance isn't coming Back from the Dead. It's regrowing [...] [tvtropes.org]