Nick Arcade Episode/Emerald Hill Zone
From Sonic Retro
Nick Arcade Episode - Emerald Hill Zone
The first and the most obvious, where is Tails? Either he wasn't implemented yet, or was deliberately disabled by Sega because he would no doubt mess up the 25-ring challenge. Also, note that this version of Emerald Hill plays Star Light music from Sonic 1!
Furthermore, Emerald Hill has a different layout from the Simon Wai prototype.
<- bridge
twisted walkway ->
The above map, created by LOst, shows the partial layout of Emerald Hill (after the first bridge) in Nick Arcade's prototype. Click for a larger version.
WARNING: The above map has parts marked in that we have no clue about from the video.