There are two worlds, each inhabited by their own set of characters. One of these worlds is inhabited by Video Game Characters. Their "master" is the Master Hand, a being that is nothing, but a right human hand. The other is the Cartoon world. Their "master" is Princess Celestia, a pony that has both a horn and wings. Neither world has known about the other until now...
In an unknown space
Tabuu: Damn! Defeated by those lousy Smashers! My plans are ruined! Huh, another world? Maybe I CAN take down both worlds together! All I need is to study that world.
One Year Later:
Sonic and his best friend, Miles Prower, who likes to be called Tails, are running to rescue Princess Peach Toadstool from Dr. Ivo "Eggman" Robotnik
Sonic: Tails, why do you think that Egg face would want to capture Peach? Isn't that Bowser's job?
Tails: I don't know Sonic, maybe he wanted to lure Mario into a trap.
Sonic: Well he sure failed in THAT objective (stops running) Hey Tails, look! (both look up) Seems like we made it to Eggman's lair.
Tails: Alright! Let's rescue the Princess
(Both are unaware that Eggman has been watching them)
Peach: Ha! Looks like you're defeated, Sonic will rescue me
Eggman: Fat chance! Get a load of this!(pushes buttons)
Tails: Sonic, watch out, Badniks!
Sonic: He doesn't get it, does he?
(After defeating all Badniks, he burst open the door to where Eggman and Peach have been watching)
Peach: YYYAAAYYY!
Eggman: Silence! Sonic, you may have gotten through my badniks, but you won't rescue the Princess!
Sonic: I will, Eggman! (Performs a homing attack onto the machine that was holding Peach, sparks come flying out, the entire ground begins to shake!)
Eggman: Look at what you've done! My dimensional transport machine is going haywire!
(outside, on a floating island)
Knuckles: The Master Emerald, it's sensing something!
(Everythin disappears in a white flash!)