Hooray for Naruto's origin story!
Though I am getting excited to see Naruto fully utilize the demon cloak like Killer Bee can. I wonder if he's going to teach him the mechanics behind transforming into Version 1, Version 2, and full tailed beast transformation or Version 3 if Kishi decides to call it that. I want to know how that works and stuff. I have a feeling that Kisame may be more powerful then anyone thinks and go up against Naruto, Bee, Guy, and Yamato at the same time.
Remember that it was a Zetsu clone in Kisame's place and I think it wasn't as powerful as the original shark man mist swordsman of the Akatsuki. I also have a feeling that Bee will be captured by Kisame and Madara would come out at the last minute and get Kisame out of there. I also think that Zetsu will capture Gaara and put a clone in his place to spy on the five great nations and the land of iron to get intel on there strategies.
No, Kisame was the one fighting, up until he used that huge water tsunami and transformed. Zetsu says that it was hard switching places with Kisame while underwater
here. It was somewhere between his transformation and the end of the fight that Zetsu replaced him.
That being said, in the flashback to when they were talking with Madara, Kisame makes several allusions to being much stronger than he showed.