Firstly, Sonic may as well not be in the real version of the SSE any more then Jigglypuff, Wolf, or Toon Link,as he just gets a random cut scene throwing him in at the end with no relevance to the rest of the story. Secondly, I’m having Sonic be playable so early because in my version of Brawl, Sonic is a starter character. If you don’t see why Sonic and Snake should be starters, go watch zero puncuation’s Brawl review on the escapist, that is all.
Inserted in-between the plains Mario/Pit level and the Rayquaza boss fight, a cutscene will occur where Sonic will see a chilli-dog out in the open. However; Yoshi also sees said chilli-dog, and they rush for it, both desiring it strongly. Sonic arrives first, being the speedy hedgehog he is, and lets out his “You’re too slow!” taunt to Yoshi, taking a bite out of the chilli dog, much to Yoshi’s annoyance. Yoshi snatches the chilli dog away from Sonic with his tounge, much to Sonic’s shock. A fight ensues between Sonic and Yoshi, you getting to select your character.
After the fight, Wario will be whoosh by and pick up the loser on his cart, adding that character to his collection of trophies while giving a taunt to the winner. Sonic will come up hastily and save Yoshi/Yoshi will save Sonic with his tounge, and Wario will be angered and proceed to flee. A level playing as Sonic and Yoshi follows, chasing after Wario on the cart, both rather angry at him.
At the end of the level, Sonic and Yoshi will have a fight against Wario, but in the end Wario lucks out as a large amount of subspace enemies happen to come by, occuping Sonic and Yoshi as Wario gets away. Sonic and Yoshi have a fight against a horde of subspace enemies. Afterwards, the next cutscene Yoshi motions to where Wario went frantically, but Sonic shrugs, Wario not being that big of a deal to him. Sonic speeds off, leaving Yoshi by himself. Yoshi shrugs and decides to take a nap on a nearby tree stump, where he is later found by Link, as in the real SSE. After this scene, the Rayquaza boss fight happens as normal.
After the stage where you play as Marth but before the stage where you play as Link and Yoshi, there will be a cutscene of Sonic seeing Pikachu struggling to defend himself against a large amount of subspace enemies as he travels about, running freely. He decides to come over and help the electric rodent, Pikachu being in a rather dire condition. You’ll play as Sonic and Pikachu against a horde of subspace enemies, but afterwards another cutscene will occur where a over-whelming amount of them arrive. Sonic and Pikachu flee from the large group, but only Sonic gets away successfully due to his speed. Pikachu is captured by the subspace army, explaining how Pikachu got in captivity in the subspace bomb factory.
At the end of the “cave” level where Mario, Pit, Link, Yoshi, and Kirby are on their way to Dedede’s castle, a different cutscene will occur. The floor will give in underneath the characters at the end of the stage, and they’ll get split up and fall into separate parts. Mario and Yoshi will fall down into one section, Pit and Kirby into another, and Link into the remaining one. Pit and Kirby’s level plays first, being nothing particularly special.
After Pit and Kirby’s level, Mario and Yoshi will have a level, and at the end a cutscene will show Sonic running full speed into Mario, causing them to crash into each other. Mario assumes Sonic is hostile and sends a fireball at him, Sonic runs around it and comes over to smack Mario. A Mario vs Sonic battle follows, you getting to choose your character. After the battle, another cutscene will show Yoshi frantically coming over to the winner, telling them that the loser was his friend. This is illustrated by Yoshi rapidly flailing his arms letting out his noises, and a flashback will come on the screen in black and white. If Mario won, the flashback will show an earlier clip of Sonic and Yoshi teaming up against Wario. If Sonic won, the flashback will be an original clip showing Mario and Yoshi fighting against Bowser. The winner of the battle understands and revives the losing character, and the two of them shake hands. Sonic stays with Mario’s group for the rest of the SSE.
After the Mario vs Sonic brawl, Link will be face to face with Toon Link. They will be very shocked at each other, and Toon Link will cower slightly. Frantic, Toon Link attacks Link in fear, both being no familiar to doppelgangers (See: Dark Link). A brawl between the two Links follows, you getting to choose your character. Toon link will comes to his senses after the brawl and revive Link if he wins, while Link will shake his head reluctantly and revive the less competent version of himself if he wins. They’ll go through a level together, and then the group will be reunited and continue on to Dedede’s castle, that cutscene happening normally.