xD I never said he had God speed. I said he's cut through Zabuza's sword and when he tries to clash weapons like when he and Kakashi clashed Kunai VS his sword, except this time, the chakra enhancement will cut through zabuza's sword like a hot knife through butter.
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Like butter? I don't think so. This is showing Killer B jumping in the air, about to slam down on Sasuke but Suigetsu blocked it at the last second so Killer B already had an edge for gaining a lot of power by jumping. Also, it cut about half of it even before Sasuke intervened, that'll give Zabuza the time to jump away.
If worst did come to worst, couldn't Zabuza just drop his sword while Mifune cuts it, jump away, then put up the mist? Nothing is stopping him. You make it sound as if Mifune will chop his sword in a second, it takes time dude. Also, once he drops his sword, as the mist is up, he can pick it up possibly hidden in the mist, and use the broken half of it (which is still large and about the side of Darui's sword" And kill Mifune with it.
I also have a theory that lightning chakra running through a weapon is more effective then just regular chakra