So why was Rayman able to beat Reflux and was he unable to beat Knaaren in the tunnels ? If you ask me it's because the Knaaren in the tunnels were with many, calm and were completely focused on Rayman. Now, Reflux on the other hand was only with myself, he was distracted by all the noise of the audience, and threw all his energy out, even if he didn't know where Rayman was ( for example, when Rayman is climbing on the sides of the arena platform ). This made him tired and in the end weak, and that's why Rayman had a chance to beat him.
These are just some thoughts I'm having, I think they're pretty correct, but of course, correct me if I'm wrong about some things