Use Silvers telekinesis when facing Shadow to pick up items and knock him down with them. If you try picking up Shadow, he'll hit you when you try and throw him. Using this strategy will eventually wear Shadow down.
First, use Silver to hurt him until his first arm guard falls off. Then, switch to Shadow and hit him with the beams until his second arm guard falls off. Next, use Sonic to defeat the rest of his first form. Finally, simply use all three to survive the blows of lasers while continuously attacking.
Choose Sonic from the Episode selection menu. Note: this works best if you have completed Sonic's part. Go to the building that is part of the Desert Stage (not the place where the Transportation Mirror is located). On the opposite side of the mirror, there is a wall. Use the "Sliding" technique to get under the wall. While Sonic is landing on the roof, Sonic should do a sideways spin instead of a normal one. Note: This may not work every time.
In Soleona, go on top of a metal box in the military base portion of the map. Stand on top and repeatedly tap X. If done correctly, you will start going into the air. The longer you tap X, the higher you will go.
When fighting Silver as Sonic, first do a slide move into him as he is falling from the sky. Then, collect a ring and run around until you hear "How bout this?" Do a homing attack on him when you hear it. Run away again until you hear "How bout this?" again and do another homing attack again. Repeat this until he is defeated.
On multiplayer mode, select Battle mode. Choose Silver and Sonic and go to any level. Get to the first checkpoint and have Sonic fall and appear at the checkpoint. However, do not move him. Then, make Silver fall and appear at the checkpoint. Just when Silver appears, freeze Sonic. He appears very small when he is frozen.
Jump with Silver by pressing A, then pressing the same button again while in mid-air. This makes Silver float around. When floating in mid-air, tap A while moving in any direction instead of holding the button down. This will make Silver jump a longer distance.
Choose Sliver from the Episode selection menu. Note: This works best if you have completed Sliver's mode. Move to the part of the pier from where as Tails or Sonic you travel to Wave Ocean. Next to the building is a barrel with no cover. If desired, go inside. This makes it easier to get Blaze in. After a couple attempts of spinning in circles, Blaze should come in. If you are near the edge of the barrel, use Psychokinesis to see Silver's head pop out of the barrel. If you have plenty of patience, you can get Blaze to be in the barrel and Sliver on top after fooling around with it.
There is a glitch in the purple gem you can buy at the market. The purple gem lets you to "change size" in the description, shrinking you down to fit in small areas. However, when using the gem for Sonic, you are able to jump infinitely. When you press Jump while holding Activate Gem and repeatedly tap A, your character will act as if he wants to do the homing attack. However, the game glitches, cancels it out, and lets you to jump as many times as desired while moving in the direction you wish to go. This lets you reach interesting parts of Soleena or an action stage that you were not meant to access. If you die or find a alternate way to lose the gem, it will be "out of stock" for some time.
In multi-player mode with Sonic, equip the red gem. Activate it and then die while continuing to hold the activation button until you respawn. After you respawn, deactivate it. You will now run a lot faster and time will slow down.
After the the video clip of the Princess of Soleanna, go through the town square towards the store, and you will see an old man with a mark on his head. Talk to him so that you can test out some new shoes he just made. He will let you keep them.
As Sonic in Story or Trial mode, choose the Silver Boss battle. Get as many rings as possible (fifteen), then go to the alley in the corner. Get as far into the corner as possible. When Silver uses his levitation technique, try to get back in the corner. Silver will use the levitation technique again and the rings will be behind you. You should be able to collect the rings before hitting the wall and dieing. Then, when you hit the wall, try collecting your rings. You will then go outside the level's boundary. You will be able to walk on invisible bridges and hit other invisible things. Silver might even also get out of the level boundary and throw you out of Soleona, causing you to keep flying forever.