My hypothetical Bowser Jr. trailer:
*SHING* *FWOOSH*
The trailer starts off with Dr. Luigi fighting an unknown opponent.
"What is this power?"
DR. LUIGI WAKES HIS PILLS!?
The screen pans over to a collapsed Dr. Mario, revealing the recent character leak to be false.
The dust settles, revealing the opponent to be none other than Ness, a long-time fan-favourite Smash veteran.
Dr. Luigi prepares to battle, and utters, "for my brother!" But Ness blocks Dr. Luigi's pill attack WITH HIS BASEBALL BAT HOLY **** SO COOL.
Dr. Luigi is about to lose, and Ness starts to charge an attack.
"PK..."
Suddenly fireballs fall from the sky, covering the battlefield with dust and stopping Ness's attack. Ness escapes the attack and looks up, revealing a shadowy figure in a flying teacup.
He jumps out and looks at Dr. Luigi. The shadowy substance covering him dissolves, revealing...
"You ruined my family vacation!"
BOWSER JR.
BRINGS THE PLUNDER!
The airship theme from Brawl starts to play.
"Bowser Jr!"
"Smash has many powerful foes, Dr. Luigi. But I am no ordinary Koopa!"
A montage of Bowser Jr.'s moves begins. "Cannons! Fireballs! Clown Car! And... paint balls!"
"Wow, you have so many weapons!"
"I can only use them so many times... Which is why I carry my paintbrush!"
"This is no time for me to stay in the operation room... I'll fight by your side!"
Short clip of Dr. Luigi follows, revealing him to be a near-identical clone of Luigi.
"Is that... the plumber king himself?"
"And the poltergust hero of legends! Worthy opponents indeed!"
They start to battle as the screen fades to black. The focus goes back to Dr. Mario, watching as the others fight.
"I guess I'll get my chance... another day..."
"NO, YOU'LL GET IT TODAY! DR. MARIO, ON MY MARK..."
Bowser Jr. and his old rival Dr. Mario gang up on an opponent for his Final Smash.
PS. Also play as the seven Koopalings!