...and their animal friends.
There is quite A LOT of fan art of Rainbow Dash with Sonic, mostly the "Modern" incarnation, I guess because they are both fast and some shade of blue.
There is an aspect of Sonic, however, that tends to be overlooked and that I think makes him, or at least his "Classic" incarnation, perfect to crossover with Fluttershy: His animal friends.
Originally, the motivation behind Sonic's crusade againts Dr. Eggman was to free the little animals trapped in the doctor's machines, who were used by the doctor as living batteries (Way before 'Matrix', mind you). The animals had distinct, cartoony designs, and according to the manuals (Meant to give background to the games) at least one member of every species had a name and was especially close to Sonic.
In this regard, I prefer the american version over the japanese version, because it states that Sonic grew up with and was raised by these seven animals, and they all teached him something.
Flicky (The bird) taught him to apreciate freedom or something along those lines, the rabbit taught him to run fast, the squirrel to jump high, I think the walrus taught him to breath bubbles under water, and the most interesting is definitely the rooster, who was always trying to fly and always ended up rolling down hills, wich inspired Sonic to spin in the ground as he does in the first game, wich would eventually lead to his classic spin dash attack.
This is why the squirrel has a ribbon, just like in the promotional art in the west (Was turned into a female, originally named Ricky and renamed Sally Acorn; some may have heard that name).
Anyway, with the 'Adventure' games the trapped animals became generic, non-cartoony ones, wich served for the Chao Garden mini-game (The games already had their share of side characters similar to Sonic); later games didn't have trapped animals, being replaced with rings or points for the "boost" attack; then the game 'Sonic Colo[u]rs' had Sonic saving little aliens instead, each kind giving him different abilities. The original animal friends then returned in the 'Sonic the Hedgehog 4' games, and 'Sonic Generation' had a mode dedicated to saving them and one of the statues was made after them (Although the rabbit, the squirrel and the walrus were saddly absent).
But anyway, I think this concept wasn't explored enough in the games, the use of these critters has a lot of potential to give depth to the character and the games of Sonic without becoming too complicated. I honestly wouldn't mind having them over the majority of the side characters.
But wathever. Fluttershy.
Fluttershy, Angel bunny and My Little Pony: Friendship is Magic © Hasbro
Sonic the Hedgehog and the animal friends © SEGA
Edit: I tried to add some light and shadows, something I'm still trying to get into; if anyone has any suggestions or advice in the matter (I'm using Gimp), I would be thankful.
Edit edit: Seems like I got my wish with 'Sonic Lost World': [link]
It's a game in wich Sonic has to save the animals from six weird aliens and Dr. Eggman, no less than in a style that reminds of the unfinished 'Sonic Xtreme'. Seems perfect to me.
I just hope they get all the animal friends (And maybe new ones?), the trailer only shows the chickens, pigs and flickys.