Why do I feel like the "blood" in Zoro and Killer's panel is actually Kaidou's clothes?
I mean it makes no sense, if Zoro or Killer did actually cut him, why did Oda don't show that to us when that would be a big feat? He showed us instead that they failed cutting his head by a bit. And the most weird reason to why I think it's his clothes is because there is no trace of blood around that "cut".
Also, the reason to why I think Kaidou became a dragon(fish) again is because in that way he can use the regeneration of the awakening that the Zoan users have in order to heal himself. I believe that all the attacks from the 5 supernovas managed to hurt him, at least a bit but with doing that he can heal and do as if nothing actually happened.