Princess Peach was Crazy-Prepared, allowing her and Prince Peasley to thwart Cackletta's plan to steal her voice before it even began. Pretty badass for a normally Distressed Damsel.
Chopper Bros.' incredible strength means that if you pay attention on your BP and ATK stats, you have a move which is devastating to early-game enemies, and downright overpowered on later bosses.
As always, reaching Bowser's Castle is a treat to play through, as you fight your way through all of Bowletta's underlings: The seven Koopalings, and Fawful.
The final battle with Cackletta, which takes place in the hellish landscape that is Bowser's stomach with background music that can be described as nothing short of metal, while the hideous towering abomination that is the soul of Cackletta unleashing lightning, fire, and everything else she has at you in one of the single most epic boss fights in gaming history.
Luigi got several of these moments.
The Mario Bros. ambush Cackletta and Fawful at the Woohoo Hooniversity. Fawful tries to get between the Bros. and Cackletta, but Luigi pounds him into the ground with one swing of his hammer, taking him completely out of the fight.
Later on, Luigi knocks Fawful out of Bowser's castle.
Dressing up as Princess Peach to fool the villains, and then making off with the Beanstar, much to Bowletta's fury.
Saving Prince Peasley from a Piranha plant.
After Mario developed bean sickness, Luigi was paralyzed by fear, but thanks to a Hypno Fool making him think he was Mario, quickly regained his confidence.
By the end of the story, the guards who didn't recognize him earlier now call him "Master Luigi".
The reveal of the Remake, which not only updates the game with Dream team and Paper Jam graphics but also includes "Bowser's Minions" a game where you control the titular characters to rescue their master! And it's just one of the great things Nintendo showed at E3.