Dark Pit’s entire character was created based Pit’s dark alt in SSBB

In Brawl, there's a trophy of Bowser depicting him in his wedding tuxedo from Super Paper Mario, with the description stating that "this might just be the last time we ever see Bowser in a tuxedo". Turns out it wasn't. Cue  Odyssey

4:09 Technically Kirby: Right Back At Ya! named the sword first. Smash used the same name afterwards, and later the name was brought into the game canon.

Another example: Joker's Standard Up-B, Grappling Hook, first properly appeared in Smash Bros Ultimate, before it was implemented in Persona 5 Royal. Royal was in development at the same time Joker's Smash DLC was made, so there was no doubt an agreement behind the scenes to use it as his Up-B. Before Royal, most people figured it came from Joker swinging on a rope in some of them menus.

4:02 Meta Knight's sword got its English name from the Kirby: Right Back at Ya anime, but it is true that the move Galaxia Darkness came from Brawl first before appearing in Planet Robobot

Also, the Star Fox team all started wearing reflectors in Zero.

Actually, Bowser's shell spin attack might have indeed originated in super smash bros melee in 2001 but I'm 100% sure that Sakurai was inspired by Super Mario World where Ludwig has this spinning shell ability.

Technically the Whirling Fortress was SMB3 as the Koopalings defensive move after taking a hit

I love when this happens honestly.
In Ridley's case, Brawl cutscene was so iconic that Ridley grabbing Samus and shoving her around became a move in all his subsequent appearances.

So with the Smash Bros. ability, that means that Smash Bros exists in the Kirby universe.

PK Flash being green originated in Melee, and became canon in Mother 3. In EarthBound, it was just a white flash.

Dedede's Jet Hammer, which was planned for the cancelled GameCube Kirby game before being added to Super Smash Bros. starting with Brawl, Kirby Super Star Ultra and Kirby Air Riders.

It's worth noting that, while DK himself never used it until Bananza, the Spinning Kong move was based on Dixie Kong.

Zero Suit Samus' stun pistol was actually introduced in Zero Mission, which came out nearly 4 years before brawl.

Kirby's voice actor, Makiko Ohmoto, first voiced the character in the original Super Smash Bros. in 1999. The "Hi!" voice clip she recorded for Kirby's taunt was then reused in Kirby 64: The Crystal Shards.

In Super Smash Bros. for Nintendo 3DS and Wii U, Greninja was given the ability to create water blades as an attack. This concept was later integrated into the Pokémon anime, the live-action film Detective Pikachu, and the game Pokémon Unite.

Another thing worth noting is that while he can use Thunder Magic and the Levin Sword in his source game, it was smash that really solidified Robin's association with the Levin Sword and Thoron

3:48 Shuttle Loop was introduced to Meta Knight's moveset in Kirby's Return to Dreamland on the Wii

Side note that's unrelated, when Meta Knight is a boss and not playable, the Mach Tornado attack is his most powerful attack, and in the older games, if you aren't able to get behind him in time, it's a gurenteed hit and it can EASILY kill you even if you are okay on health. And he goes pretty much all the way to either side of the screen and you hardly have anytime to rush over there, the old games purposely have him jump as far away from the other side of the screen as possible. Kirby bosses tend to just dump out attacks in rapid succession and he has another attack that has the same prepping animation as Mach Tornado so you might assume it's the weak attack and not react. I think Meta Knight's Mach Tornado in Super Star and it's remake did like a quarter or half of your health.

Once the 3D games came out this attack was massively nerfed unfortunately.

For the Dedede hammer we actually already had a move where Dedede use a rocket hammer to make a spin in Kirby Super Star but the idea of the reactor hiding in a normal hammer is completely original.

3:47 Shuttle Loop has been a move used with the Wing ability since Super Star, actually. Smash was just the first time it was given to meta knight. Also, im fairly certain that the Galaxia sword was named in the kirby anime years before brawl came out.