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The Nick Arcade prototype version of Sonic the Hedgehog 2 is the earliest known pre-release version of the game, predating the famous Simon Wai prototype. This prototype receives its name from the game show Nick Arcade due to an earlier version of Sonic the Hedgehog 2 being showcased in two episodes where its build seems similar to the latter prototype, if not the same version as used on the show.
Notably, this prototype shows that Sonic the Hedgehog 2 is based off of the original Sonic the Hedgehog. For example, the Emerald Hill Zone in this prototype uses the same music as in the Star Light Zone.
If Sonic runs into a wall while running at a fast speed, he will bounce back off of the wall. This feature was scrapped sometime after this build, but the sprites it uses are still present in the Simon Wai prototype.
Sonic and Tails are in different symmetrical designs on the end signpost.
Each Zone uses music from the original Sonic the Hedgehog.
Tails can lose rings for the player if he is hurt.
If Tails dies, the camera will follow him as he respawns until he goes off-screen.
If Sonic and Tails are hit at the same time, lots of rings will sprawl out regardless of how many rings they actually have (provided the player has at least one ring).
The backgrounds of Hill Top and Chemical Plant don't move.
When obtaining Invincible, stars are not seen but the music still plays. The music and invulnerability both last until the end of the act.
Green Hill Zone
Despite this Zone being in the original Sonic the Hedgehog, it appears in this prototype with the correct format for Sonic the Hedgehog 2.
Because this Zone was originally in the original Sonic the Hedgehog, and the collision detection is different in that game from Sonic the Hedgehog 2, Green Hill's collision detection is very glitchy. However, the collision detection for the entirety of the original Sonic the Hedgehog is present in the ROM and can be accessed through a variety of cheat codes. Unfortunately, while this does fix the collision detection in Green Hill, it breaks it in all the other Zones.
Tails Life Monitors are present just as one is in Hidden Palace Zone, as all the monitors in Green Hill Zone haven't been changed to use Sonic 2s' monitor system. As a result, nearly every monitor in Green Hill Zone has been "switched" with a different monitor.
The springs from both Sonic games appear in this zone. Only the Sonic 2 springs appear in the released version.
Many badniks and obstacles use glitchy sprites, including rings.
The Crabmeat badnik uses a lost sprite from Sonic 1.
The rings' glitchy sprites from this zone will be carried over to Marble Zone if the player advances to the latter zone.
The spike placements are identical to Sonic 2's final version. The sprites appear glitchy during gameplay but the template is mostly identical when using Debug Mode.
The boss for the zone also uses glitchy sprites, as well as using the same lost sprites as the Crabmeats in place of Robotnik's face.
Tails can stand on the spikes without getting hurt.
This is Chemical Plant Zone, and it is heavily under development, with major differences in the level's design from either final or the later prototypes, and is very unfinished.
Marble Act 1's terrain layout and background are identical to Chemical Plant act 2 and act 3. The latter two's object placements are copied from Green Hill Act 1.
It uses a pink palette instead of a green palette used in the later betas and final versions.
Some of the buildings in the background are shorter, and match that of the footage of the Nick Arcade build.
Extra objects and the falling block from Chemical Plant are accessible for this zone with debug mode. However, the former's graphics appear to be incorrect.
The transportation tubes were apparently used in a different way, but they aren't functional in this build.
Spring Yard Zone
Actually Hidden Palace Zone, the zone layout is as it is in the later Simon Wai prototype.
The object layouts of Green Hill Act 2 are carried over in Spring Yard Act 2.
Act 3 includes water, which appears after the player exits the tube. The water repeatedly falls and rises throughout the level. This level's starting position is inside the blocks, therefore the camera will appear faulty unless the player presses a few buttons.
The location of Green Hill Act 1's rings are carried over to this zone regardless of which act.
The Labyrinth Zone's music is heard if the player triggers the countdown while under water in Act 2 and Act 3
The water level can be controlled using the 2P controller.
If you move the water up so a badnik is submerged, his orange spot turns bright yellow. This is because Sonic's underwater palette is really from Labyrinth Zone in Sonic 1.
All of the Debug Mode objects besides rings and monitors have broken previews.
There is a strange bouncing object using the bat's graphics found in the debug list.
It has two objects that uses the animals' graphics. One only flips, the other flips and shoots fire.
There is no terrain to be found in Labyrinth zone. Even if there is "terrain" the images and data appear to be faulty. However, the ring locations of Marble Zone, Chemical Plant's background, and the rippling effect can be found here. Labyrinth's Act 3 is a copy of Scrap Brain act 3.
Star Light Zone
Actually Emerald Hill Zone and is as the same as it was in the Nick Arcade video. The layout is very different in Act 1, and slightly different in Act 2. Star Light Zone's music plays in this zone.
This is the only zone where Tails is disabled, suggesting this particular version was tailored for the Nick Arcade show in order for the contestants not to have their rings lost by Tails, as well as hide the fact that he can follow the player, as this feature hadn't been directly featured previously. Tails can play in this zone via 2 player mode, though.
The boss behaves exactly the same as in the later prototype, but it does have explosion effects. These are the same as the ones from Sonic 1.
The player is almost unaffected by the orbs that the fourth Buzz Bomber onwards shoots.
Scrap Brain Zone
Actually Hill Top Zone, this zone is also under heavy revision, as it finishes with a pipe leading to instant death because the screen-limit has not been changed yet.
The playfield limits are still the same as they were in Sonic 1, but the level does not end at these limits. As a result, Act 1 cannot be played through.
The secondary collision array for Act 2 is missing, so as a result, loops do not work.
Second act crashes at about the midpoint. This is because, as Sonic 2 is built off of Sonic 1, the level event handler calls a subroutine from Sonic 1 that no longer exists (the transition between Acts 2 and 3 of Scrap Brain Zone). Final Zone crashes at the second tree for the same reason.
The lava does not hurt the player in this prototype.
Green orbs are used as the weight on teeter-totters instead of a Sol without fireballs.
The lifts are not fully functional yet and partly broken
Letting Tails drop down at the end of Act 2 will still force the player to the next Act.
Act 3 also has no terrain, but the color palletes are still correct. The top exit for Scrap Brain Act 3 is impossible to reach.
The Hill Top Zone's terrain and background layouts are positioned on the rightmost edge of Scrap Brain Act 2, in the same place as the Final zone. Because the boss data for Final Zone has been deleted, the game will crash and a pink screen appears if the player advances past the second tree. If the player uses debug mode in this area, repeatedly pressing the button on a Sega Genesis console while the screen is pink will create an "illegal instruction" error. The error's graphics are incorrect however.
Same as Sonic 1
Unplayable (crashes to lila)
Playing music in the sound test and then selecting this has a 46.8% chance of carrying an infinite note
Sprite (Nick Arcade/Simon Wai)
Sprite (August 21+)
Changed eye shape of Sonic's and shading to the top of it.
Added flesh-colored eyelids.
Added shading to the top of the eye without changing its shape.
Twelve frames of animation changed to eight frames.
In the Nick Arcade and Simon Wai builds, when Sonic runs, his shoes and legs go into a cartoony blur. This was toned down in the final version to just affect his sneakers.
Sonic's skidding starts out with a new unique beginning, before reusing a few frames from the original Sonic the Hedgehog. It then turns around and starts pushing in the other direction. The final two frames will loop until Sonic either stops completely or does a different action.
In the early prototypes, Sonic's hands move but his body stays level, unlike in the original Sonic the Hedgehog. The final sprite splits the difference and moves the body and hands in different frames. Oddly, there is orange coloring on his shoes, because the sprites were based off of the previous game sprites, plus a minor coloring oversight.
The balancing animation is just a faster version of the one from the original Sonic the Hedgehog, with an added head shine and an orange mouth due to sprites being based off of previous game's sprites. The final game adds four new balancing animations based on how far Sonic is from the edge and whether or not he is facing the edge.
Sprite (Nick Arcade/Simon Wai)
Sprite (August 21+)
An added shine to Tails' spinning sprite.
Sprite (Nick Arcade/Simon Wai)
Sprite (August 21+)
Its head was redesigned to be less ant-like, more detail was added to the abdomen, and the jets were straightened out.
Sprite (Nick Arcade to Aug. 21st)
Sprite (Sept. 14th Prototype)
The Crawls' lack any kind of walking animation, only being able to put its shield up in one direction.
Sprite (Nick Arcade)
Sprite (Simon Wai+)
Only the Robotnik signpost remained unchanged in later prototypes and the final version.
The Egg Scorcher Mk II in the final game can shoot out fireballs, but those fireballs grow and shrink in size and have three frames of animation.
Unused sprites of Sonic turning.
Sprites for Sonic moving faster than the final game.
Another set of sprites for Sonic moving faster. Although Tails does have a full-speed animation, the only change is his twin-tails using only two sprites.
Animations of Sonic pulling something, having some puzzle elements related to this were originally planned.
An unused animation of Sonic balancing on a ledge.
A background element depicting a cavern obscured by stalagmites and stalactites. Although it is seen in old screenshots for Hidden Palace Zone, it is never seen in any prototype released.
Animated tiles. The source code suggests that was meant to be loaded in Chemical Plant Zone Act 3 with original cut boss being called "vacume".
Animated tiles using the Chemical Plant palette. No foreground tile-based propellers or water exist in the final game.
Some sort of burning piece of an object.
The Hill Top Zone one-way gate. Although identical to the one in the final game, it has no code available.
Graphics for a Hidden Palace Zone object.
A dissipating cloud.
The switch which later be used in the final game. It does not have a discovered code.
A spinning metal ball, which was seen in early concept art. It would have acted as an obstacle that continuously bounces around the floor in a high arc around random places damaging the player when touched. While it did make its way to the Debug Menu in the 2013 remake, it uses a different palette (as this was its alpha Version) and explodes once it floats above the playable character's head.
An unfinished Badnik named, "Bubbler's Mother". It would have flown around the level dropping particles on the floor that would turn into Bubblers. Its concept art shows that it was originally intended to be seen in Chemical Plant Zone. These also appear in the Debug Mode of the 2013 remake.
The Bubbler enemies being dropped by Bubbler's Mother. They would have stuck to the floor for a bit before exploding into three bubbles.
Sprites of possibly rocks or clumps of sand found in the Crawl's files. It seemed that it used to have an underground attack where it would pop out of the ground and hurt the player.
The Batbot Badnik with different pallet colors.
The Octus that appears in Oil Ocean Zone. Originally, it would have fired a shot at Sonic/Tails and then fly off screen as it despawns.
A Stego Badnik that would have appeared in Hidden Palace Zone. It slowly moves back and forth, and activates its thrusters when Sonic approaches it to charge right into him.
A crocodile-like Badnik. As it moves back and forth, it opens its jaw when it faces Sonic/Tails.
The Aquis Badnik, from Oil Ocean Zone. After it moves back and forth and shoots one shot at the player upon approach, it slowly jumps downwards to its official Y coordinate.
Another variation of the Aquis, named Skyhorse. All the features it has between the two is still the same, just having a different body with a rocket on its back instead of a fin.
A BFish Badnik, which would have leaped instead of acting like the Chopper Badniks in Emerald Hill Zone. They were originally planned for Hidden Palace Zone.
All four of the monitors still in early versions of the game.
The standard static Monitor that does nothing upon it being broken. Compared to the final game though, it damages the player.
The Eggman Mark, which possesses the same function as the static Monitor.
The Mystery Monitor, which also does not work in this build.
The lamppost from Sonic the Hedgehog, which are placeable in Emerald Hill Zone and Hill Top Zone.
Code 52, resembling the moving blocks in Marble Zone, Labyrinth Zone, and Scrap Brain Zone. The code was recycled to be used on the moving platforms in Chemical Plant Zone.
In the episode of Nick Arcade featuring the prototype, a younger Melissa Joan Hart is seen playing a brief section of this prototype. In this challenge, she had to collect 25 Rings in Emerald Hill Zone Act 1 in 30 seconds.