Classic Disney Shorts/WMG

Junior from "Bellboy Donald" is Minnie Mouse and Pete's son.
He has black fur like Pete and Minnie Mouse. He has ears like Pete, but with Minnie's ear size. He has a flesh-colored facial "mask," body proportions, and eyes like Minnie (save for the eyelashes) but is completely tailless like Pete. His feet are bigger than Pete's feet but smaller than Minnie's huge feet. He has a muzzle like that of Minnie, but shorter, smaller, and with a lip shape like that of a cat.

The real reason why Mickey and Minnie aren't married...
...is because Mickey has the hots for all the Princesses.

How did that happen? After visiting Disney World, seeing the Princess floats in the Main Street Parade all pass in order, seeing Mickey's float and hearing this quote (he says it with a flirty tone, too - also, paraphrasing): "Didja see all those princesses?" Then adds quickly, "No one like my Minnie though!"

Why'd he date Minnie for so long? He didn't want to have his fame crash and burn over bestiality charges.
 * Mickey wants to marry a princess because of the perks of being royalty. True, he's made millions upon millions in merchandising alone; perhaps he became a money-hungry jerk over the years who wants a crown to be adorned upon his head. Also, what stopped Jessica from marrying Roger Rabbit (even if only he made her laugh) despite being different species?
 * The Princesses probably want in on the Mouse's money, too.
 * He IS royalty.

Mickey and Minnie ARE married.
They just keep up the youthful appearance of being boyfriend and girlfriend to appeal to each new generation.

What with all the various stories and places and time periods they've been in, it's possible to say that they married each other in each one, but we just never got to see it.

They were clearly married in Mickey's Christmas Carol and Kingdom Hearts.

Then after the happy ending, someone pressed the Reset Button, and poof! they're back to square one. Donald Duck and Pete are prime suspects here.

And besides, why would a mouse find a human princess attractive anyway?

Truth in Television: The previous voice actor to Mickey was married to the current voice actor of Minnie. They're the only people in the world who know what Mickey and Minnie sound like having sex.

The classic characters (Mickey, Minnie, Donald, Goofy, Clarabelle, Horace, Max, e.t.c.) are of a species capable of Regeneration.
This explains why their appearances have changed over the decades.

Gastly from Pokémon is biologically similar to the classic Disney characters.
His appearance has changed very much over the years.

Mickey Mouse is a robot
Theres a similar theory for Sonic (Dr. Eggman is a Predacon!), so why not?

There is two Oswalds a Universal one and a Disney one.
The Universal one convinced Mintz to get rid of Walt Disney along with his Oswald the Lucky Rabbit and slowly replace him with the universal one. Yen Sid, Walt's unknown alter ego, saved the Disney Oswald by creating The Wasteland