Oh man...it's been eons since I last did anything fan fiction-wise, whether that means reading it or writing it. Nice to see a fellow author here.
I read through what you've got on your Super Mario Bros. fic so far, and I like your interpretation of the events that led up to the games. Except......you got a crucial detail wrong. Pauline and Peach are two entirely different characters. After the events of Donkey Kong, Mario broke up with Pauline for whatever reason and decided to pursue Peach instead at around the same time he switched professions to a plumber. I don't know whether you're aware of that, but I have to say that your misinterpretation of that particular detail from the games set the stage for a very exciting story. Still thought it was worth pointing out, though.
I don't have time to read all of your Mario and Sonic fic at the moment, but I did go through the first chapter, and have a few points to make. Mostly, I think you're not quite portraying Yoshi correctly. There is no official answer on a lot of the intricacies of Mario's world, like whether Yoshi (commonly accepted to be a guy) can lay "live" eggs - or whether Yoshis even have genders at all. But I think you were a bit too direct with the situation of Yoshi giving birth in the egg basket - it's a little sick, and I think unnecessary. Also, I've never heard of Yoshi egg omelets - leaving the question of whether Yoshi's eggs are "live" or not aside, they'd have to be for an omelet to be possible. But then, I don't think he'd willingly sacrifice his own young so it can get cooked. It's a bit of a technicality, but it does raise some disturbing ethical questions. Oh, and Yoshis are proven to be able to speak normal English.
As for the positives, your writing is rather fluid, which I find impressive in today's age of "lulztalk" and what have you, but I'd strongly suggest you work on making things a bit more interesting through the use of more adjectives and especially more detail in the dialogue sections. You start going "back-and-forth" in those very quickly, and not only does it leave a somewhat vague image in the reader's mind, but it also can make for a confusing conversation in which you lose track of who's talking.
That's it for now. Hope you don't mind some friendly critique - you didn't say you didn't want any. 
Of course I don't mind any friendly criticism, it's what keeps authors going! Although I do have a few explanations for your points...
In Super Mario Bros, I'm trying to completely revamp what the Mario universe is (ex. Toadsworth being King, and Bowser originally being human.) Princess Peach disguising as Pauline is just a way to keep the story moving, and in my opinion, is a unique way to explain how Peach met the Mario Bros.
As for Yoshi, I wouldn't really take the whole "giving birth" thing too seriously. Just picture it like this: Yoshi was laying his eggs like he normally does (no birth involved,) but Toadette made it more awkward by suggesting that Yoshi was technically giving birth, even though he wasn't. The whole Yoshi egg omelet is also just something I wouldn't take seriously.
Thanks for the compliments about my writing techniques, and I assure you, it gets quite a bit more interesting as the chapters go on. Chapter 1 is just a sample really, the writing gets much more complex as you delve deeper into the story. Thanks for the feedback!
