"Like any other other warrior." You should take out one of the others. There's some grammar errors that make the story a bit hard to read in a place or two, though that may just be me, a few places you need to fix capitalization, like names, but otherwise this is great

I like the description, though I see one issue. The characters are lacking...well character. I have played Smash Bros, the latest one as well as the Nintendo 64 version, so I know what's going on, but maybe add your own background to the piece. Why are the character's there? You action scenes are great, though there are a few places where the flow just isn't there as well as it could be, and the formatting itself seems a little strange. Instead of indents, or making what looks like a huge paragraph with an indent inside of it, why not just separate the paragraphs with a space in between them, it would be easier on the eyes. There's also a few small errors, like in the last paragraph, there's a place you didn't capitalize Little Mac. Not trying to nitpick, just a bit of advice, up to you whether you take it or not.

Wow! So, to start off, I have played Smash Bros before, and my brother has the latest one, so I have a lot of background for what's going on. You're quick to the punch with your action, but that doesn't mean that you forget all your description either, and the scenes come to life before my eyes. I'd look for a beta reader to check for inconsistencies here and there, but overall it's a great work, and I'd like to see more of it.

Hello Comrade,
After reading the first two bits you've written here, I can offer some feedback.
Action is definitely your strength here, and although the grammar and semantics needs a little editing, I can easily visualize what's going on. Of course, being a fan-fiction, it doesn't hurt that your characters are instantly recognizable.
But ... and it's a big but ... the most important thing in writing a story are the characters. Characters are key. You only need to spend a little time on it, but you should establish early WHY the characters are in the arena.
For example, being a gritty SSB story, perhaps Diddy-Kong needs money (or bananas) to pay his bitch wife for child support, and after retiring from the big leagues, he's decided to come back to the street fights to earn some extra bananas. 
Little Mac can be like a 'Rocky' character, an underdog who takes the Diddy down. Maybe Diddy can't believe it at first, but sees an opportunity to make some serious bananas by training the young buck into a superstar?
If we don't understand the character's motivations for doing what they do, then we can't get invested in their story unless we are already fans of SSB.
Anyways, continue writing. I'm looking forward to seeing what you do with it.
-JV