Good game, but...
You should NOT add more than 2 Sonic Characters in this game. I mean for real, there are soo many other characters you could have added instead of them. Also, the hit tests are kind of glitchy. For starters, characters slide as if they are fighting on a sheet of ice. There is no friction on the ground, so every time I want to turn, I end up sliding off the stage. I know you're trying to make it more "realistic," but gameplay is something that you should be focusing on.
Second, when two character or enemy sprites collide into each other, they pass through each other like ghosts. Something else that is kind of frustrating. Perhaps you can also create two different attack keys for regular and special moves. Another problem is the fact that Master Hand's attack where his fist flies vertically downward is very unpredictable. His fist should be high enough so that the player knows where it's at. Not only that, but he should pause for 1 second before slamming his fist down so that it's actually possible to dodge the attack.
Third of all, in Smash The Targets, there's this one target that moves soo fast that it's pretty much impossible to hit it. It took me literally one minute to chase that target and to smash it. Perhaps you should lower the speed of the targets?
Those are the only concerns I will share because I only played through classic mode once. So once again, less Sonic characters, better player hit test, less broken Master Hand, and slower moving targets.
This review will probably be negative due to stupid Sonic fanboys, but I will rate this 8/10. Good game, just a couple of glitches that make it frustrating.