Beta Elements: Level Order

An interesting aspect of any video game, at least in the eyes of avid fans, collectors, and developers, is the development process, and the elements that get changed or scrapped along the way. Sonic the Hedgehog has these as well, and if you are familiar with the Level Select Code, you can see evidence of such changes right away. Entering the following code:

US/EU Version:

 Up, Down, Left, Right. A ring sound will play - holding A+START will bring up the menu.

Japanese Version:

 Up, Down, Down, Down, Left, Right. A ring sound will play - holding A+START will bring up the menu.

The Level Select screen allows you to choose from any level in the game, including the Final Zone. It also lets you start at the Special Stage, or use the Sound Test to listen to the audio. One thing to note here is the level order shown. It lists Green Hill first, which is perfectly normal. It then lists Labyrinth Zone before Marble Zone, despite the fact that Marble is the second Zone, and Labyrinth is the 4th. The same order seen in the Level Select is also reflected in the Sound Select. The first six tracks are the background music for the levels, in the same order as the level select. Code and arrangement of data within the ROM all but confirm that this was the original order, but this was likely changed due to the perceived difficulty of the levels.

One thing to take note of, though, is the specific order of these levels, in comparison to the sequel titles. This sequence suggests a tropical level leading into a water level, followed by a level within ancient ruins and an urban-themed nighttime level after that.

Sonic 2 Level Order

Emerald Hill (Tropical level) > Chemical Plant (Water... semi) > Aquatic Ruins (Ancient ruins) > Casino Night (Urban nighttime theme - Based on Vegas casinos) 

Sonic 3K Level Order

Angel Island (Tropical level) > Hydrocity (Water) > Marble Garden > (They even share a name!) > Carnival Night Zone (Urban nighttime theme).

S3K mirrors Sonic 1 even more, with the 6th zone taking place at one of Robotnik's bases.

The placement of Labyrinth Zone and that zone's similarities to Sonic 3K's Hydrocity Zone immediately clued me into this pattern, and the comparisons between Marble and Marble Garden are easy to notice. That's not to say that these games are "clones" of the original, as they made great effort to make the subsequent zones stand out on their own. It's just interesting to think about how Sonic Team clearly had a blueprint for how to construct Sonic's world, not unlike how many Mario games tend to follow Super Mario 3's World order.