Who would win?

I don't know, why are they fighting? What's at stake? Where are they fighting? Why are they both there? How much are they allowed to use their environment to their advantage? If not at all, isn't it unfair on a fighter whose strength is adapting to their surroundings? Are there others present as possible collateral damage one or both of them may or may not care about? Can they walk away from the fight or are they forced to battle to the death? Who's forcing them and why? Is it to the death or until one gives up? Can they take breaks or is there a time limit? If the fighters are beings capable of using tools and weapons, are they allowed to use them, and what kind? Can they ask for backup? Inspiring loyalty and making allies is a highly useful survival skill - if it's a strength of one of the fighters, are they allowed to utilize it? If not, what's preventing them? Can they use it on their opponent and convince them not to fight? Can they team up against whoever's making them fight? Can they just sit and chat instead of fighting if that would be more in-character?

This is why I'm bad at these.