Big Foot:Sonic gets first dibs of course. Big Foot will fly around shooting bullets at you. simply move around the shots and eventually he will land. After landing, Big Foot will shoot missles. dodge all of them. once he stops shooting the missles, run up and perform a homing attack on the cockpit. if you have the ancient light attack with Sonic, you may be able to use it to hit Big Foot while he is still flying.
Eggman: now you get to face a well known rival with Tails and his new Cyclone machine. basically all you need to do in this fight is just rapidly shoot at Eggman while trying to stay alive. this is by far the simplest fight in the entire game.(and the same for the Dark side of the story facing Tails).
Shadow: now Sonic and Shadow meet up again, this time to fight. the easiest way to win is to NOT use the homing attack. simply use your rolling attack (fire roll if you have that) when his back is turned. using homing attacks may cause you to lose.
King Boom Boo: now Knuckles can finally fight. first off run and drop your jaw because this will very likely be the first time you notice how fast Knuckles really runs. you are being chased by a giant ghost, proud of yourself? make sure that Boom Boo can't catch you. he will start throwing blue fireballs attempting to hit you. but with Knuckles going twice the speed of Sonic you have no need to worry. after a while Boom Boo will stop to blow fire. quickly run behind him and hit the hour glass. Boom Boo shrinks and sinks into the ground. stepon his Shadow and then dig. now just keep up with him and punch him once. now he will move faster, but if you are quick enough you can get another hit. after the first hit, when you hit the hour glass, Boom boo's shadow will go into the wall. repeat the process to win.
Egg Golem: the object of this fight is to get behind the golem. if you do you will see platforms coming out its back. jump up these platforms. you will now see much smaller platforms coming out the back of its head. use the homing attack on these to help you get up to the generater. hit the generater with a homing attack. repeat the process to win. the golem will attempt to punch you, spin and chop you, and head bang you in this battle.
Rouge:ok you fight in that weird tyower thing from Meteor Herd. your best bet would be using the drill dive for this fight. in this fight Rouge can use her Black Wave attack like in multiplayer. simply drill dive her over and over until you win.
Eggman round 2:ok. in this fight Eggman has all the upgrades for his machine. this in my vision is one of the hardest fights in the game. shoot Eggman as much as you can in this. give him no chance to recover. Eggman also has his Rocket Launcher and Power Laser. best bet is to get him near the bombs in this little arena, and shoot them. it may take a few tries to get this one right, but its worth it after beating him.
Shadow round 2:run foward and don't stop because the platforms you are crossing are constantly falling. the cheapest way to play this fight is to let Shadow ahead of you just enough to where he will use the Chaos Spear. once he says "time to put this to an end", spin dash at him to dodge the Chaos Spear and hit him. repeat doing that and the fight will be a piece of cake.
Hot Shot: check Bog Foot on Hero Side for details on how to win. the difference is the fact that this one will charge up and shoot a giant laser ball at you. stay away from the cross hair and you will be fine.
Tails: look at the first fight with Eggman on Hero Side for details on how to win.
Flying Dog: same as Big Foot and Hot shot except the fact that this one does not land. use Rouge's ability to climb up the fencing on the sides of the platform. from here glide over top of the cockpit and drill dive, or just glide into the cokpit. there is basically nothing to it.
Sonic: look for details on the first fight with Shadow on Hero Side.
Egg Golem: in this fight you are aiming for the weak points with the vulcan cannon/bazooka. the weak points are the cracks in the rock on the golem. shoot them out and machinery will appear. target and shoot that. there are about 3 weak points, good luck.
Tails round 2: look up deatails in the Eggman round 2 fight for Hero Side.
Knuckles: look up deatails for the Rouge fight on Hero Side.
Sonic round 2: look up details on the Shadow round 2 fight on Hero Side