The Sonic the Hedgehog 2 AutoDemo is a Sega Game Gear EPROM cartridge demonstrating the then-upcoming release of Sonic the Hedgehog 2. It was sent to several magazines worldwide for preview purposes. On July 14, 2014, Orengefox obtained a copy of the AutoDemo, and the ROM was released to the public in August.
As the name may suggest, this Sonic 2 AutoDemo is not playable - instead, the demo plays itself, starting with a simplified introduction sequence and title screen (much like the final game), before continuing with Sonic running through an early version of Green Hills Zone (complete with loop), gliding through a largely empty Sky High Zone, and briefly riding one of Under Ground Zone's mine carts. Following this, a static "Coming Soon" screen appears, and the demo loops from the beginning.
A single music track plays throughout the demo - one not present in the final game. Much is different from the retail release of Sonic 2, most notably the introduction and title screens and the Green Hills Zone tileset. Tails is also completely missing.
Many early screenshots of the game shown during development are thought to originate from this demo - the primary giveaway being that as gameplay is always the same, the ring and time counts at specific points never change. Furthermore as the HUD resets at the start of each of the three sections, Sonic is seen using a hang glider mere seconds into play - in the final game there are no opportunities to use one this early.
The AutoDemo has an internal date code of 1991-12-05, nine months before the final's date of 1992-09-05.
- The SEGA screen is different and plays no "SEGAAA" chant.
- The title screen only features Sonic, who has no animation (but rises from behind the ribbon). Similarly, the opening cutscene merely shows Sonic running.
- Neither the introductory cutscene nor the title screen play any sounds.
- Sonic's physics are completely different and almost broken. He gains speed instantly and slowly goes through walls. It's also hard to turn Sonic when falling or launched by a spring.
- Sonic, instead of running then pressing down, can also spin by pushing down, then left or right.
- Sonic also can move freely when spinning.
- The minecart wheel sits above the rail, rather than inside.
- The lightning flashes in sky high zone are different, and are in the priority plane (i.e. in front of the Sonic sprite). Rain is also displayed in front of Sonic.
- Sky High's raining act has a deep pool of opaque water at the bottom that is not present in the final game.
- The art of Green Hills Zone is completely different, being more similar to the credits sequence of the final version; however, early versions of the layouts for acts 2 and 3 are already present.
- Sky High Zone didn't have trees or flowers in this prototype and seems to be an earlier version than the one featured on the magazines.
- Under Ground Zone has many tiles that didn't make the cut, including gray bricks and curvy stone pathways.
- Only Green Hills Zone, Sky High and Under Ground Zone have artwork in this prototype; all other zones either are not present in the prototype or do not have any associated tiles yet.
- The sound of jumping on a spring is the same as the "rolling down a hill" sound.
- The "rolling down a hill" sound ends with a cartoonish pitch shift.
- No sound is made when falling.
- Badniks, bosses, end of act panels, chaos emeralds, and monitors are all entirely absent. Explosion graphics are present in the ROM though.
- The zone order is noticeably different from the final game: Green Hill and Sky High are the first two zones, followed by several acts with no data (trying to load these acts results in a blank screen). Under Ground Zone is played next, followed by what appears to be a single act of an extremely early Gimmick Mountain. Aqua Lake, Scrambled Egg, and Crystal Egg are not present in this prototype, but would most likely have been the third, sixth, and seventh zones respectively.
Following a standard Game Gear "Sega" screen, a brief, Sonic-only intro before the title screen.
Sonic is dropped into a very different Green Hills Zone and begins running to the right, occasionally jumping, collecting rings and using a ramp.
He runs around a heavily scripted loop, before exiting mid-stage.
Sonic then handglides through a very empty Sky High Zone for a while.
Then he falls and lands on an Under Ground Zone mine cart, which rolls down a hill.
Finally, a "coming soon" screen appears and the sequence repeats.
A hacked version of the ROM exists that allows manual control of the game. It was created by MarkeyJester.
Following release, the ROM was quickly disassembled with control restored to the player. Traversing the stages further reveals a number of hidden and non-functioning objects, such as springs (of which only the vertical types function), spikes and breakable walls, as well as more of the prototype tileset and artwork.
Green Hills Zone is much longer than what is usually shown and almost resembles a completed stage. Under Ground Zone utilises several tiles unused in the final game, including what is thought to be a tube (similar to those found in Sonic 1's Green Hill Zone) and some sort of building. Sky High Zone has bridge-like platforms; unfortunately, these do not function in this build, and Sonic falls right through them.
Given the very early state of the code, there are many bugs affecting Sonic's movements. Loops do not function correctly in several ways (entering at the wrong speed, entering the wrong direction, etc), less control is afforded to the player while on springs and Sonic can roll simply by ducking and pressing right or left (i.e. there is no initial momentum requirement). It is impossible to take damage, though falling (or jumping, if near the top) off-screen will usually trigger a reset after a few seconds, and exiting the playfield on the right pushes Sonic several pixels to the left in an unclean fashion.
Many sound effects are incorrect or nonexistent, and the music track never changes. Hills do not affect Sonic's speed in any way, making some areas with rings impossible to reach, and the ring and time counters in the HUD have no effect on the game when they max out.
Normally, only three stages are shown by the Autodemo, and only the first act of Green Hill Zone can be played in the hacked version; however, Retro user MarkeyJester developed a tool that allows the ROM to be modified to place Sonic in a different level by typing in a hexadecimal code for each zone and act. (Zone 00 Act 00, for example, would be the Green Hill Zone act displayed in the Autodemo.) Using this tool, there are eight playable levels, not counting levels that can be played with more than one designation. The following levels are either at least partially playable or manage to load the HUD:
- Zone 00, Act 00: Green hill zone, the stage displayed prominently in the Autodemo's first moments. This is probably the only level that Sonic can completely traverse by normal means, due to the demo's odd physics and numerous bugs, though it cannot technically completed due to the absence of an end of level sign.
- Zone 00, Act 01: Another Green hill zone act, which appears to have a similar (not identical) layout to the final game's Green hill zone act 2. Some areas will trigger the loop animation in spite of the visible absence of loops.
- Zone 00, Act 02: An early version of Green hill zone's boss act. Unlike the final game, there is a curved tunnel (similar to Sonic 1's Green Hill zone) towards the end of the stage, and the very end of the stage (where the boss would presumably be fought) is flat, unlike the bowl-like shape of the final game's boss area; Sonic can find another 'ghost loop' in this part of the stage.
- Zone 00, Act 03: An early Sky high zone stage.
- Zone 01, Act 00: Same as Zone 00 Act 03
- Zone 01, Act 01: Another Sky High level
- Zone 01, Act 02: This Sky high stage occurs in a thunderstorm, similar to act 2 of the final game, and is displayed in the Auto demo. Unfortunately, Sonic does not start with a hang glider when controlled manually, causing him to immediately fall to his doom in a deep pool of opaque water, similar to that in Sonic 1's bridge zone. Repeatedly trying to jump may make Sonic start running on thin air; using this glitch to explore the level reveals a single cliff on the right side of the stage.
- Zone 02, Act 03: An Under Ground zone stage with stacked rails, a tube, and a number of buildings.
- Zone 03, Act 00: Same as Zone 02 Act 03, but Sonic starts in a minecart (which he quickly loses).
- Zone 03, Act 01: The last stage shown in the autodemo under normal circumstances, Sonic starts in a minecart, goes downhill, and goes off the hill. The game will freeze if Sonic falls far enough.
- Zone 03, Act 02: Sonic starts in a falling minecart and falls for several seconds before the game locks up. Note that Sonic will not respond to button prompts while falling in the minecart.
- Zone 03, Act 03: The full HUD, along with a single minecart wheel (but curiously not the entire minecart) near the top of the screen, appears, but the rest of the screen is a glitched mess of light blue with darker blue triangles, and the game resets within a few seconds. Possibly a very early version of Gimmick Mountain in view of the background palette and the aforementioned minecart wheel (Under Ground zone also has minecarts, but has a different, much more red background palette).
- Zone 04, Acts 01 and 02: The ring and time counters appear, but the rest of the screen is a glitched version of the title screen.