Being a Sonic the Hedgehog gamer, as well as a person who actually fully plays Sonic Battle and nearly every sonic series game, I got to say, Shadow is a better choice than Tails, and he doesn't even need to be a clone at all.
Even in SA2, Sonic and Shadow were quite different with their own running speeds, and different styles. Though they have a couple of similar moves, Shadow was never a real clone. The only one amongst that game that could be considered a clone was Tails, as all he was was a heroic verison of Eggman. Shadow proved to be extremely different from his own game, as well as Sonic Battle.
Shadow performs extremely different moves in Sonic Battle, making him his own character and not a clone of Sonic. The only similarity in the game was pretty much their running speed, and he's still faster(but harder to control)
A good way to put this is comparing Falco to Falcon. Falcon and Shadow are both quite strong, and extremely fast, but super hard to control. Falco is still very fast, but relatively easy to control. This is the basic comparison. Also, Sonic is much weaker than Shadow, but originally sported a few more moves, giving him an advantage only in options.(Bounce Attack, basically) Here's my comprehensive move list for Sonic, based loosely on Sonic Battle and Sonic The Fighters, with a couple of other games.
A: Punch(a very basic forward punch)
AA: Kick(same as the punch, but a little bit more sideways)
AAA: Top Kick(he puts his hand on the ground, and kicks forward, much like a strong soccer kick)
Forward A: Over Punch(he swings his fist in a similar fashion to a spinning side kick)
Up A: Ring Toss(he tosses a ring slightly upward, dealing a small ammount of damage with decent knockback)
Down A: Sonic Spin(he simply spins on the ground, dealing a slight ammount of damage. Constant pushing of the move makes is somewhat stronger, with a bit more knockback. He doesn't move anywhere, though)
Smash A: Flare Kick(using his hand, he does a spin kick arching forward that circles around the ground. He then lands backwards. While the afterlag is bad, the attack is quite strong with decent enough knockback)
Smash Up A: Up Draft(pretty much the same as Fox's Up Smash)
Smash Down A: Windmill(quite similar to DK's Smash Down A from the 64 version. Only his feet spin, though, looks stupid, of course)
Dash A: Slide Kick(he slides forward with a kick, fairly similar to Mario's dash, but he looks a bit different)
B: Wave Fire(more or less a Falcon Kick, but as a projectile. He jumps backwards when he's done, much like when Falcon hits against a wall. It works the same way for the Air version)
Forward B: Ring Dash(same as Fox's forward b, but shorter)
Up B: Homing Attack(he does a high arch spin in the air. If a character is there, it targets them instead, as he will an item. If it hits a character, he can do it again, but only in the same direction, thus making it less broken)
Down B: Bounce Attack(much like how DK can't use down b in the air, it works the same way on the ground. He bounces straight downward, but can jump out of it if he has a jump left. It doesn't provide infinite jumps of course)
Air Neutral A: Kick(a basic diagonal kick with little damage)
Air Forward A: Fire Shield(he moves forward while on fire, which doesn't go far, but makes him immune to pure fire attacks(as Flare Blade would not be blocked, as its both Fire and a Sword being used))
Air Up A: Electric Shield(he jumps up slightly with an electric shock, and becomes immune to pure electric techniques)
Air Back A: Shield(a small blue shield appears over him as he spins. It does little damage, but can clash with other attacks fairly easily)
Air Down A: Eagle(a weak spike that is hard to hit, but has decent power. Weak in damage, but not in knockback)
Z: Grab(as Magic Glove sounds nice, it seems a bit too strong as we all know that it has extremely huge range. Thus, this doesn't crappify the technique's expectations)
Z + A: Fire Punch(he punches his victim with a bit of fire on his hand)
Z Forward: Spin Fire(he spins into them, and sends 'em flying, fairly similar to Wave Fire)
Z Up: The Ringer(he slams a ring into them, throwing 'em upward, but not very far)
Z Back: Spine(he throws his spines into the opponent, making them inch back. Good damage with very little knockback)
Z Down: Foot Stomp(originally from Sonic The Fighters, he stomps their foot, immobilizing them for a 2 seconds of gametime. However, Sonic has a bit of afterlag to even it out)
Taunt: Finger shake(he shakes his finger as the screen)
Win Taunt 1: "That was cool!"(he shouts this out as the screen as he waits in his SA2 stage finish, complete with the original music from the games)
Win Taunt 2: Yaah!(he does a ton of spins and homing attack as a homage to his Team Blast from Sonic Heroes)
Win Taunt 3: "Nice try, Eggman!"(basically says this while looking at the screen...okay, worst one, I know)
Now for his stats.
Jump: 4
Speed: 5
Power: 3
Defense: 4
As for colors, they can be a simple as different shades, but none needs to be Super Sonic itself(as in his hair flopping up, etc. A simple plain yellow hue works)
That's all I've got, and since this isn't a Shadow thread, I won't do his.
