The intro features Sonic riding a surfboard into Angel Island Zone. In the final game, Sonic rides the Tornado, jumps off, and turns into Super Sonic. The surfboard Sonic object still exists in the final game, but goes unused.
The only way to see this intro is if you wait on the title screen for the demo. Getting into Angel Island Zone Act 1 normally does not play the intro.
Knuckles also has completely different sprites, and simply blocks Sonic's path instead of punching him out and stealing the Chaos Emeralds. Because they share the same palette, Knuckles also causes the HUD text to turn green; the developers actually implemented two different fixes for this in the final game: Knuckles was given a different palette, which uses yellow for his socks instead of green (and, oddly, pinker shades of red) plus in this particular scene the HUD isn't even drawn at all anymore.
Outside of the intro cutscene, this version of Knuckles can also be seen during gameplay, standing a short ways in front of the player at the beginning of Angel Island Act 1. He leaves after a few seconds of standing and gesturing. If the player walks forward before he leaves, he glitches out when the player gets near him. The exact way in which he glitches varies; if playing as Sonic, he turns blue due to the badnik palette loading over his, and if playing as Tails, he turns into a mass of incorrect tiles.
These Knuckles sprites, possibly before he was redrawn to be more in-style, are completely different from the other cutscene sprites used throughout the game.
Tails does not seem to spawn into the level for a while, aside from flying above the first badnik. The player can be airlifted by Tails, interestingly.
A fire shield and badnik right before the miniboss are missing.
Underwater countdown timer graphics do not load correctly.
In the debug list, there is a strange object that seems to test sprite scaling. It causes some very adverse effects on the game, its level collision, and its VRAM.
In one of the upper alcoves early in the level, there are 2 static monitors that hurt the player when broken. These were replaced with monitors containing Power Sneakers and 10 Rings in the final game.
The area before the miniboss has a few tiles incorrectly placed.
The miniboss cutscene is slower, rougher, and the miniboss plays a different sound when launching missiles.
The second part of Act 1 loads much more slowly, leading to some garbage object graphics at first.
The waterfall platform objects do not play any sounds.
Act 1's boss arena has the decorative flame objects like final, but they load incorrect graphics.
During the tunnel to the end of the level in Act 2, you can see for a moment when the flying ship graphics are loaded.
The HUD pauses for the entire duration the flying ship is present, and it resumes once it leaves. This was scrapped in the final because it also stalls the ring counter from refreshing, should the player get hit by the ship's bombs.
Eggman's "whooshing" sound when he goes through the trees at the end is completely different.
The sound that plays when Eggman burns the bridge is different.
The boss palette tends to cause issues with rings.
Even if you jump off the bridge while Knuckles destroys it, you still go to Hydrocity Zone anyway.
Angel Island Zone Act 1 Map
November 3rd
Final
Angel Island Zone Act 2 Map
November 3rd
Final
Unfinished cutscene
In addition to the surfboard cutscene, an early version of the final intro does exist in the prototype ROM, as shown in the embedded video. It can be enabled using the PAR codes 003CC6:0003 and 003CC8:5AD2. There are a few differences:
Some of the graphics are glitched.
The Tornado doesn't bob up and down while flying.
The final Knuckles object is present in addition to the prototype one. However, he doesn't jump up to uppercut Sonic (although it makes Sonic lose his super form), which softlocks the game because it leaves the player unable to move.
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