- Sonic needs to be unlocked
As a foe, Sonic is one of the hardest in the game. Be prepared to pick the proper characters to fight this guy because his high speeds are unmatched by anyone. Sonic is often considered to be one of the cheapest characters in the Super Smash Bros. Universe, due to his high speed and repetitive moves, leading some tournaments to not allow Sonic to be used as a playable character at all.
One of his weak points is if his spring is used on the ground, everyone can use it! Also, he suffers from a lack of good kill moves.
Sonic is not only very fast but also an incredible jumper. If you are battling a large opponent then stay in the air where most of there attacks are less useful. His forward aerial attack does good damage and your back areal attack sends the opponent flying. Sonic's homing attack is very useful if you are versus another fast opponent as it makes you hard to hit and you will probably hit the opponent.
The two rolling attacks are good as it is hard to damage sonic as he roles towards you and you can still jump to get over holes. Sonic's jump is very good for recovery and the spring that falls can do minor damage to enemies below. When facing a Subspace Emissary Mode boss, try this: jump, >+a (optional), ^+B, v+a. this a pretty nice for racking up some damage.
Basic Attacks
Special Attacks
Taunts
Final Smash
Super Sonic: Sonic summons the seven Chaos Emeralds and turns into Super Sonic making him able to fly over the stage. When you are transformed into Super Sonic, you can tackle your enemies and blow them away with a high velocity strike. This move works best if the opponents are on a flat area so that you can hit them repeatedly without worrying about them getting away. If you are having trouble with people that endlessly air-dodge, just hover next to them and wait until the dodge ends, then charge them. This is one of the longest Final Smashes, clocking in at eighteen seconds.
Match-Ups
Wolf
For starters Wolf is pretty fast, but no worries! He is also no as fast as you if you are playing as Sonic. Wolf's delay after he is dashing is sorta the same as Sonic's, they have a lot in common. Just dodge his lasers and remember that he is strong and fast too. Sidestep his lasers and run up to him then GRIP, if you can grip him at the very edge throw him off then use dair (in air down attack, jumpX2+up super smash+down air attack) on him while he is trying to get back to the stage. Thats all.
Mario
This will be quite a difficult fight, as Mario has many tricks up his sleeve. If you knock him out, he can do his b+forward and just get back in. His aerial attack will give him a huge advantage, as Sonic is not very good at aerial. Just keep trying to attack him with fast moves. Don't stay too close to him; stay at a mid range and wait for him to come to you. If hes using an aerial attack, use up+b and then down+a. That will most likely hit him and deliver good comeback, but beware if this misses Sonic will be very vulnerable.
Luigi
Falco
Falco is similar to Fox and Wolf, but any good Falco player is skilled at using his differences. Falco's laser his stronger and slower than Fox's, but not as much as Wolf's. If he is using it on you just use the Side Spin move. The hop at the beginning will stop any lasers that hit you, allowing you to reach him easier. However, due to his Reflector you will have a hard time reaching him. To counter this you will have to employ a strange feature of the Side Spin move. What you do is begin charging it up, but about halfway through the charge hit the standard attack button and let go of every button (including the control stick). If you did it right, Sonic will do a really fast leap forward that will send him about the distance of a long Homing Attack. This will allow you to approach him without being subject to Falco's Reflector and lasers. From there, knock him off the side of the stage since Falco falls fast and has bad vertical recovery. If you have Falco off-stage, jump after him and hit him with an aerial attack (avoid using +) and then Spring Board back to the ledge. However, beware of chain grabs! Falco's chain grab can easily rack damage up on you if you can't escape it.
Ness
Lucas
Pit
Pit is a good match up for Sonic. Sonic is one of the most aggressive characters in the game, with an array of fast attacks, while Pit is by far the most defensive, with two reflectors, spamming projectiles, a regular A Spam and incredible aerial mobility. Pit's defensive nature can cut off most of Sonic fast attacks and can make approaching a difficult task, even for Sonic.
Fox
If you're against a good fox user don't use your rolling charge against him, he'll just A+> and potentially get a free kill. Try to stay close to him as you should be able to combo him continuously with faster moves. If he gets away, wait for him to come to you unless he starts using his blaster. In that case, try to just run at him and hope you can time a dodge past him when he begins to do one of his kicks. If you're good with your dodges this fight should be easy, if not you'll more than likely lose.
Lucario
Should be easy to defeat any Pokémon especially this one. Just use final smashes, Smash Attacks and the Grab attacks but Beware of the damage you deliver. The higher the Damage the stronger Lucario gets.
Kirby
Kirby on the other hand is a harder one. He can suck you up and spit you out if you dare to use spin dash on Kirby. Regardless, use your final smash if you have the chance. His stone and hammer attacks are powerful. If he uses his rock attack, try to dodge and use the opportunity to dash in for a grab.
Snake
Snake is one of the most powerful characters. His basic and special attacks have very dreaded results which is a high KO rating and his grenades can be thrown back to him if you pick it up carefully and quickly.
Sonic
Sonic against Sonic? That is insane and difficult much due to both Sonics will run pretty fast and attack pretty fast. The one thing to be aware about is the final smash which makes your enemy invincible and faster and will take you out within seconds.
Meta Knight
Since Meta Knight doesn't have any long range attacks and his close range attacks are devastating, use hit-and-run tactics. If possible, do this: Go to one end of the stage and use Down-B. Hold it there until Meta Knight is just about on the ground, and release. This works best on Sonic's stage. If you acquire any long range items, use them as much as you can. Ray Guns and Star Wands, probably.