I actually once had the idea once to make a Smash Bros fangame where all characters would have exactly the same mechanics they have in their original games. It wouldn't actually be just canon, but characters would work exactly as they do in the original games. It'd be impossible to balance due to how different everyone works, but if nothing else it would be a fun experiment.
Mario would need to jump over his opponent three times to win, but he can only take two hits and he's gone.
Mega Man can do nothing but Jump and Shoot, but would gain an additional move if he defeats his opponent once within the match.
Link would be based on Adventure of Link, having sword stabs, sword beams when at full health, and up/down stabs when holding up/down in midair. Also a magic bar and a bunch of spells.
Samus would likely be OP even if she purposely does a **** amount of damage and takes a lot of damage. All of her abilities, the speed at which she can shoot, and having infinite jumps that deal damage on contact would make her pretty much undefeatable.
Kirby would not have any moves other than a sliding kick unless he copies his opponents. Instead of gaining a specific move of each fighter, he has a few generic abilities that are assigned on what fits best. For example, Link and Marth would both make him transform into Sword Kirby, and both Samus and Fox would make him Beam Kirby.
Marth would be complicated as ****. Basically, he could only move by selecting a spot on the stage with a cursor and he'd automatically move there. After moving, you can select to attack in any of four directions. If you manage to attack in the correct direction at just the right time to catch your opponent within the square you pretty much win the match because there'd be a transition to a FE style match on which the opponent can't do anything. Since this **** would be so ridiculously difficult to land, this is a one hit kill against any character. If you fail, your turn ends, and won't resume until your opponent makes any kind of attack. While Marth is stuck in a turn based-system, he still takes damage in real time, and will die if his life reaches 0 even if it's currently his turn. He'd be pretty much screwed against characters with projectiles because they can just avoid him whenever it's his turn. Also Marth VS Marth battles would be ****ing moronic because the first Marth who moves is the winner, lol. To make things a bit more fair for him, if he takes damage while he's not in his turn, and his opponent is within range of the four squares, he gets to counter attack Fire Emblem Style. That'd make Marth ****ing useless against projectile-based characters, but completely broken against melee based ones.
So yeah, this would be pretty fun to see, and I once even started programming it. I got Mario and Megaman's physics down, but never even made the multiplayer, which was the whole ****ing point. Got bored, never got back to it.