Sonic 2 Beta ROM vs. Final ROM - Green/Emerald Hill Zone

Left: beta version, Right: final version

Green Hill Zone has snail robots, which are quite similar to the Motobug robots from Sonic 1, whereas Emerald Hill (in the final version) has Coconuts robots.

Left: beta version, Right: final version

Missing spring. There are a number of other small changes to layout and object placement, which I won't go into detail about.

Left: beta version, Right: final version

In the beta, Robotnik's car is stationary when he lands in it, and the wheels appear in front of Sonic. In the final, the car is moving when Robotnik lands on it and the wheels are behind Sonic.