We still haven't seen events yet. I wonder what events would exist if we got them. I can't really think of any on my own right now.
I've got some ideas..
Rivals Royale: Beat Nintendo's greatest rivals in a free-for-all.
Player: Any
Opponents: Bowser, King K. Rool, Ganondorf, Ridley, King Dedede, and Wolf
There's Too Many: Beat the entire Fire Emblem cast in a 1 vs. 7 match.
Player: Any
Opponents: A team consisting of Marth, Lucina, Roy, Chrom, Ike, Robin, and Corrin
Attack of the Clones: Beat the cast of Echo fighters.
Player: Any
Opponents: Daisy, Dark Pit, Lucina, Richter, Chrom, Dark Samus, and Shadow (I'm cheating, but we know he's coming)
A Space Odyssey: Team up with the Star Fox team to take down Ridley, Dark Samus, and Wolf.
Player: Samus
Opponents: A team consisting of Ridley, Dark Samus, and Wolf
New Kids on the Block: Show these new kids who was here first.
Player: Ness
Opponents: Young Link, Lucas, Toon Link, Bowser Jr., and Inkling
Brains over Brawn: Show these meatheads that your mind is your greatest weapon.
Player: Mewtwo
Opponents: Captain Falcon, Snake, Ike, Little Mac, Ryu, and Simon
Horde Encounter: Looks like that Honey really did the trick.
Player: Pokemon Trainer
Opponents: A team consisting of four Pikachu and one Pichu.