Birth of the Smashers
Long ago, there existed beings of unimaginable power who guarded the dimensions. However, a war struck and two of these beings which were brothers battled against one another. Soon, these beings were convinced that there was no harmony in the dimensions, only fighting and strife. The two brothers, ashamed of their own behavior, created a prison using a powerful relic of their kind and sealed themselves and the relic within the prison.
A thousand years later, three other beings appeared within the prison. Ganondorf, who's soul escaped into the prison after being defeated, Mewtwo, who in his thirst to prove itself the powerful being in existence teleported there and was defeated by the older brother who called himself Master Hand and Boswer, who was mysteriously transported there. At first, they embraced their destiny alongside the hands. However, Bowser learned through time to use the relic, convinced Mewtwo and Ganondorf to join with him and brainwashed Master Hand.
Bowser then used the relic to creat a dimension built for fighting and brought the heroes of the other dimensions. They were Mario, Link, DK, Yoshi, Samus, Kirby, Fox, Pikachu, Luigi, Ness, C. Falcon and Jigglypuff. These fighters passed through the challenges then faced off against Master Hand who pretended to be the one behind their troubles. The battle was tough but he was defeated by a combination attack between Mario and Link. The heroes then returned to their dimensions using the relic.
Realizing that the plan failed, Bowser, Ganondorf and Mewtwo deceived the younger brother, Crazy Hand by telling him what happened to Master Hand and manipulated him into bringing the heroes along with the others heroes. These new heroes that arrived with the ones that face Master Hand were Peach, Young Link, Zelda, Popo, Nana, Falco, Pichu, Marth, Roy and Bowser, Ganondorf and Mewtwo whopretended not to know what's going on. Hafway through the challenges, Bowser disappeared, brainwashed Crazy Hand and revived Master Hand. At the end, they fought Master Hand then Crazy Hand joined Halfway through the battle. The heroes were being overpowered until Master Hand was defeated by Roy and Crazy Hand was defeated by Samus and C. Falcon. As the relic appeared to them again, Bowser claimed it and alongside Ganondorf and Mewtwo, revealed themselves. Bowser then absorbed the relic, Ganondorf and Mewtwo and transformed into Giga Bowser. The fighters were outmtched until the Hands joined the battle, giving them the advantage. Giga Bowser was then defeated but the dimension was collapsing. The hands, heroes and the three villains then united their power with the relic's and recreated the dimension.
The dimension was then called the Smash Realm. The Hands, realizing the errors of their exile, then invited the heroes to join them. The Hands then built the Smash Mansion and allowed the three villans to join as well, but not before punishing them by making them clean all of the toilets in the mansion which were unfortunately very, very dirty.
The Hands then built residences and opened the gateways to the Smash Realm, allowing people from other worlds and dimensions to come and lived there. They also came to watch the heroes and villains fight for glory, honor and recognition. The group were then called the Super Smash Brothers.
The Hands kept an eye on the dimensions, postponing tournaments so the Smashers could resolve a crisis in the Smash Realm or any other dimension. But, still there was peace between these worlds.
This is just the background story. If you have any questions about any changes excluding Dr. Mario and Mr. Game and Watch, let me know.