The premier should have more characters than the original game had, but not too many. I think Mario, Link, Kirby, and Pikachu all need to be in the first 4 showed. Similar to Brawl, they start fighting
Samus should quickly appear of course with her bombs and lasers.
Fox would also appear using his blaster.
Ridley would come from the sky. He starts to attack everyone except Samus.
Starfy comes to the aid of Kirby and shows a fighting stance against Ridley. Ridley taunts and Starfy unleashes a final smash on him.
Geno should start by coming to Mario's aid. Showing off a few of his moves as well.
Little Mac should appear next to Link's help. He'd show a variety of punches on Pikachu.
Lastly, Mewtwo should appear to aid Pikachu. He'd enter by shooting down Little Mac with his shadow balls.
Megaman should be last for the surprise of course. This would really top off the trailer.