I have discovered a new technique named Downsmashing. It's where a player get another player/CPU off the stage and presses Down + A right above them. There are some characters who can and can't do it.
Characters who are known to Downsmash:
Link (a suicide mission since he keeps falling at the same position)
Marth
Ike
Mewtwo (Tested and seen in Nintendo Direct Mewtwo Trailer, he downsmashed Villager)
Lucas (Seen in the Nintendo Direct Lucas Trailer, he downsmashed Olimar)
Wii Fit Trainer
Characters who are known not to Downsmash:
Luigi
Mario
I haven't tested all the characters but here is Mewtwo downsmashing Sonic.
Characters who are known to Downsmash:
Link (a suicide mission since he keeps falling at the same position)
Marth
Ike
Mewtwo (Tested and seen in Nintendo Direct Mewtwo Trailer, he downsmashed Villager)
Lucas (Seen in the Nintendo Direct Lucas Trailer, he downsmashed Olimar)
Wii Fit Trainer
Characters who are known not to Downsmash:
Luigi
Mario
I haven't tested all the characters but here is Mewtwo downsmashing Sonic.