help for finding a sonic battle spriting tutorial.

[Ultimecia]

Maybe you should try the big robots as bases, like Omegas/Gammas/Whatever-Greek-Alphabet-You-Find, not a skinny small Sonic. Sonic IS small if you compare him with regular human beings at his games, and I believe the marines would be HUGE thanks to their armors.
The shading needs some heavy work too, but try to fix everything else before moving on.