Maybe you should add Mephiles or Mecha Sonic (use the smbz spritesheet) for a boss.
Also, an useless question: How long does it take to create a Sonic FC spritesheet?
I tried Johny's Sonic, Shadow and Silver and they were great :D Also you forgot to add Neo Sonic. http://www.mediafire.com/download/lwmmz3j9z0x/neo_sonic.zip