I can't really say, I think I read somewhere that the reason for Muu dying was due to Joki boy, but IDK. If they went at it again, i'd have to give this to Muu, I don't really see how the Mizukage beats him.
It's no point saying you think Muu would win. Kishimoto has showed us that they are of equal strength so it would be a draw. Stop being fanboys of Muu just because you think he can beat him when Kishi has showed they are of equal strength.