Well, it's moveset time.
Assuming this thing would play like Marvel 3...
Mario (If any attack is similar to Smash then I'll just say which it is)
-Normals-
Standing LightThe punch that he uses when you press A in Smash. Press it 3 times and he will do his usual 3 hit combo. Hits mid.
Standing MediumHis tilt forward attack. Hits mid.
Standing HardHis smash forward. Hits mid.
Standing ExchangeHis up smash. Hits mid.
Crouching LightHis tilt down attack. Hits low.
Crouching MediumA regular kick with long reach. Hits low.
Crouching HardHis smash down attack. Hits low. Knocksdown.
Jumping LightHis neutral air attack. Hits high.
Jumping MediumHis up air attack. Hits high.
Jumping HardHis backward air attack. Hits high.
Jumping ExchangeHis forward air attack. Hits high. Knocksdown in the air.
-Command Normals-
-> HardHe takes out a hammer, raises it over his head and hits the opponent with it. Hold the button to charge, fully charged it's unblockable. Hits high.
Down forward MediumHe slides like in his dash attack in Smash. Hits low.
-Specials-
Fireball (QCF attack)
Shoots a bouncing fireball to the ground at angle, the angle and speed depends on the button used. Hits mid.
Super Jump Punch (DP attack)
Mario jumps with his fist raised, if the opponent is hit coins come out of them. L version hits 3 times, M version 5 times, and H version 10 times. Hits mid.
Mario Tornado (QCB attack)
Mario starts spinning with his fists stretched out, dealing damage if he's touched. The button pressed determines the distance he travels. If the button is mashed he'll rise a little. When used in the air, the distance traveled is much shorter and diagonal, but hits high instead of mid.
Cape (RDP attack)
Mario takes out his cape and swings it forward. If it hits the opponent, he is turned around, but if it hits a projectile it is reflected. Hits mid.
Hover Nozzle (QCB Exchange)
Mario takes out FLUDD and uses it to hover around the stage until his water runs out.
-Hyper Combos-
Mario Finale (QCF 2 attacks)
Exactly the same as brawl. Hits mid.
Stomp (DP 2 attacks)
Mario jumps on top of the opponent, like he would on a goomba, koopa, etc. Hits high and can hit opponents that are on the ground too.
Starman (QCB 2 attacks) (Level 3)
Mario punches the opponent. If it hits, there will be a cinematic where Mario will jump, revealing a hidden block with a Starman which he will grab, then he runs toward the opponent and sends him flying when touched and numbers representing points show up, Mario then juggles his opponent the same way until he gets a 1-up (with its iconic sound of course).
I wanted to add a move with the SMB3 suits though but 4 supers is a bit much =(
-Assists-
Fireball, Super Jump Punch, and Hammer.
For this to work I think Capcom would have to use a pocket fighters art style for the street fighter characters
Ok that would be awesome. It'd have to apply to everyone though, including the Nintendo side.