I know most the sprites from are ported over from the original Sonic the Hedgehog Game Gear but the custom sprites I think fit the style of S1 GG pretty well. The custom sprites look like they were made by Sega and Ancient! (Ancient made the Game Gear and SMS version of Sonic 1) My only issue is that it would neat, if the title screen had custom sprites matching the SMS/GG Sonic 1 title screen. Otherwise great hack, you should check it out!