The confrontation between Bowser and Donkey Kong; Bowser has a gun that transforms the characters intro trophies. Diddy Kong doesn't understand the danger he's in, so Donkey Kong performs a Heroic Sacrifice by knocking Diddy into the air Taking the Bullet Bowser aimed for Diddy, transforming him into a trophy, all to protect his buddy. Aw!
The friendship that forms between Samus and Pikachu is sweet. Samus is the "I Work Alone" type, and since she's human and Pikachu is a Pokemon, it makes her look like Pikachu's trainer.
Especially her face when she sees Pikachu being basically tortured in the machine. She takes in about a second of seeing the little guy squealing in pain and promptly responds with a non-verbal HELL NO and smashes the glass.
And what does Pikachu do the second it's released from being tortured? Jumps in front of Samus with cheeks sparking, ready to defend its savior from the R.O.B.s attracted by the alarm.
When Ness realizes the Dedede badges that revived him and Luigi belong to Dedede, he immediately decides to revive him. This for some guy he doesn't even know!
On that note, there's also Ness and Luigi helping Dedede up after Wario attacks him. This doubles as a CMoF on Wario's part.
Ness again, he jumps in to save a kid he just met. Then he pushes him out of harms way not knowing if he'll be revived or not! Ness is a real sweet kid.
Whichever scene you play ("Mario's Misunderstanding/Link's Misunderstanding") is kind of heartwarming in a way. Mario gets it if he sees his princess's trophy apparently dissolve at the hands of Link, and rushes in to try and avenge her. Whereas if you play Link, he's the one charging at Mario, who then has to avoid becoming a plumber-kebab. Either way, it's nice to know how much they both care.
Dedede! Boy, was he a surprise! First he gathers up as many heroes as he can in one place to make a hero team. Then he gives up the one thing he knows can revive trophies for one of the princesses. Near the end of the game he gives Kirby a Bear Hug!
The friendship between Pokemon Trainer and Lucas, particularly their handshake after Lucas's Crowning Moment of Awesome blowing up Galleom's arm to save himself and PT.
After defeating Tabuu, you see the entire playable cast (or at least, all those you saved) on a cliff, overlooking the ocean where the Great Maze area of Subspace was, with the main theme blaring full blast. Then, the credits cut in, with an epic medley of the credits theme of the original Smash Bros, the main theme of Melee, and a piano solo of the main theme from Brawl, all while bits of cutscenes that correspond to the mood of the music play in a little box on the screen.
The music is great, and now knowing the lyrics, its meaning is clear.
The fact Diddy Kong forces Fox and Falco to help save his friend Donkey Kong is sweet. For Donkey Kong, at least.
The fact that neither of the protest much indicates that they really don't mind helping. Falco's thumbs-up to Diddy is proof of that.
When Link and Zelda find Ganondorf's trophy, they share a glance with each other before reviving him. Ganondorf is shocked by this, and while he considers attacking them the moment they turn their backs on him, he decides against it and instead follows them to fight Tabuu.
Mega Man finally showing up in the series, because many fans asked for him, so they gave the fans what they wanted.
Keiji Inafune, often called "the father of Mega Man", stated that he was "ecstatic" that Mega Man was added to the roster. He also said that he was looking forward to playing as Mega Man and beating his own kids in the game.
Even better, Mega Man's Final Smash involves summoning fourotherMegaMen to help him.
The reason behind Hideo Kojima asking Snake to be in Brawl? His kids are fans and they wanted to see one of their father's characters in the game.
As a secret unlockable character, Luigi usually isn't revealed until after the game is released. However, seeing as how it's The Year of Luigi, they decided to give the man in green the spotlight for Super Smash Bros. 4 early, further showing that Nintendo hasn't forgotten about Mario's younger brother.
Kirby and a Luma dancing together at the end of Rosalina's reveal trailer. They even hi-five with their stubby arms!
Meta example: in the wee hours of the morning on February 1, 2013, Melee successfully raised over $90,000 as part of a competition to be concluded in the EVO fighting game tournament for 2013. Brawl barely hit three digits. Why? Brawl fans turned out to support Melee and unite behind that game instead of their own. Reasons aside, this event has dramatically cooled tensions between two factions in the Broken Base.
Although that's likely an instance of the Spoiler Effect.
The old red biplane from Pilotwings and the new seaplane from Wii Sports Resort in flight together is pretty epic. It represents two generations of Nintendo in one place!
During Snake's codec conversation about Luigi, Snake instantly argues in Luigi's defense when AI Colonel starts mocking Luigi.
The Invitational Tournament at E3 2014. This coming together of fans and creators alike, all together for a show of sportsmanship and camaraderie, with everyone in a good mood.
Special mention to the crowd's reactions to Mega Man, especially once he finally managed to get his Final Smash offnote Prior to this, the crowd had mostly been low-key during this portion of the tournament. (and subsequently winning the fan vote by a landslide after that match). It really says a lot about how much the Blue Bomber is loved when his fans cheer him on despite doing relatively poorly throughout the Invitational.
KoreanDJ deserves some respect for helping that moment happen. If he had not moved Rosalina into the line of fire (apparently on purpose), Rock's attack would have missed.
Pac-Man joining the fight is cool for different reasons, but someone else put it best when describing what his inclusion means for Smash Bros. and Nintendo (also counts as an Awesome Moment):
"Whether you're a fan of the character or not, with the introduction of Pac-Man, Nintendo just pulled the video-game equivalent of "Who Framed Roger Rabbit." This is an incredible achievement that should be noted
This means that Nintendo has pulled off something unheard of - something no other company has come close to accomplishing. They have brought together four gaming legends that each started the entire industry from four separate corners of the art form. Mario from Nintendo, Sonic the Hedgehog from Sega, Megaman from Capcom, and Pac-Man from Bandai (Namco). These are four characters and companies that made the very foundation of what gaming is today, and now, in one giant collab hosted by Nintendo, they will all be in the same game together for the first time to fight it out in a celebration of the art.
This is literally on the same scale as Bugs Bunny and Mickey Mouse being in the same scene together from the movie, and will probably never happen again for a long time. Nintendo literally blew E3 out of the water culturally with this. So yes, the hype is very high, but the weight of this should drive it even higher! +1 Respec' for the Big N."
Chrom, Robin, and Lucina are still True Companions as in their source material, fighting in each others' names. Even though he's not playable, Chrom still fights with Robin for his/her Final Smash. And as in the game, female Robin could be Lucina's mother and male Robin could be her husband, adding another layer of closeness between the characters.
Anyone who's played through Awakening knows how close and protective Lucina wishes to be of Chrom. To see her rush right at Captain Falcon and Robin coming to both lord's aid can cause a tear to form.
Sakurai asked Ubisoft for some artwork of Rayman for trophy reference material. Ubisoft gave them a 3D model rendered specifically for them.