Sonic the Hedgehog (iOS, 2013)

Finally, for once, a version of Sonic 1 that isn't a straight-up emulation, Sonic Jam and the really lackluster Game Boy Advance version aside. Powered by the fan-made Retro Engine, this version features smoother animation, achievement/leaderboard support, and the ability to choose between three playable characters.

Incidentally, this version was released as an update to the existing iOS version, which was an emulator + ROM. But there's more...

Level Select
Start a "No Save" game and choose a character. On the SEGA logo screen, tap the letters S-E-G-A in that order once the entire word appears. If done correctly, you will hear the ring chime. Then hold two fingers on the bottom of the screen and wait. After the title screen appears, you'll be taken to a Sonic 2-style Level Select.

To select a Special Stage, set the sound test value to 01-06 and select Special Stage. If Max Emeralds is set to 7, selecting 07 will pick the otherwise unused seventh Special Stage.

There are several options aside from selecting levels and the Sound Test (they seem to become unlocked in the options menu though when you beat the game or perhaps fulfill other special requirements):
 * Player - Choose between Sonic, Tails, Knuckles, or Sonic and Tails (like Sonic 2).
 * Spindash - On or Off, like the Settings menu.
 * GND SPD Cap - Ground speed cap on/off. "On" simulates the original game.
 * AIR SPD Cap - Air speed cap on/off. "On" simulates the original game.
 * S1 Spikes - On/off. Toggles the infamous no-invincibility-frame spikes from the original game's initial release.
 * Items - S1, S2, S1+3, or S2+3. Seems to control what monitors appear. Selecting an option with "+3" gives Sonic the ability to use elemental shields and the insta-shield move from Sonic the Hedgehog 3.
 * Max Emeralds - 6 or 7 Chaos Emeralds. Choosing 7 allows all three characters (including Tails) to transform into their Super forms once you get 50 rings and double-tap the screen. The 7th Emerald is cyan in color. Some of the Emeralds also change color when toggling this option to match their modern palette.

Debug Mode
Play sounds 01, 09, 09, 01, 00, 06, 02, 03 (the US/European release date of the original Genesis game) in the Sound Test. During gameplay, tap the upper-left corner of the screen to access debug mode. To change the item you are placing, press the + or - on the top of the screen.

Interestingly, the debug mode allows placement of many, many items that are not present in the main game. It seems the developers looked into the unused content from the original game, finished coding them, and left them unused. This cut content may have been meant to be restored in this port, but ultimately re-cut at the request of Sega as was the case with the 2011 Sonic CD.

General

 * Unused monitors - same as those present in the original game.
 * S - works like in Sonic 3, giving Super Sonic.
 * Robotnik - shows an image of Robotnik. Like Sonic 2 and 3, it hurts the player upon breaking it.
 * Debug monitors - used for toggling new features on the fly.
 * Spikes - shows an image of spikes. Breaking it plays the "hitting spikes" sound and toggles Sonic 1 spike behavior.
 * Three Shields - shows an image of the elemental shields from Sonic 3. Assumed to toggle the Items option, but it doesn't work on the fly.
 * Chaos Emerald - Plays the sparkle sound from Sonic 2 for Super Sonic. Assumed to toggle the maximum Emerald count.
 * Image of 4 Robotniks - also present in the original. Adds collision to several platforms that don't have it normally. When placed, it acts like an invisible platform. A variant with images of Tails exists in Final Zone.



Green Hill

 * Rolling ball - is now a functional object, unlike in the original game. It rolls down hills, can crush enemies, and can break through walls. You can push it to give it additional momentum and make it roll up hills, but it can crush Sonic if it falls on him.
 * Splats the Bunny - jumps around near a set spot or jumps in a set direction. Oddly, it doesn't seem to be affected by the rolling ball.

Marble

 * Sideways spikes - also seen in the original.
 * UFO - placing it makes a bunch of UFOs show up in the sky, as they did in early photos and footage of the original game. They fade in and out of sight and are merely a cosmetic addition.

Labyrinth

 * Goggles monitor - breaking it gives Sonic goggles which only appear when you're underwater. It increases the time period Sonic can spend in water without air, and it breaks off Sonic's head like a shield if hit. The graphics were taken from the original game, though the function of this item was presumably changed: Dean Sitton stated that the goggles were originally just a cosmetic graphic.

Special Stage

 * Prohibitory sign - deletes items it's placed on.
 * Extra life icon - from the original.
 * Zone icons: - don't do anything. A blue "Zone 7" icon was added for this port.
 * "W" block - doesn't do anything.
 * 7th Chaos Emerald - Cyan, and it allows Sonic to transform into Super Sonic. However, there's no way to actually get it normally. It can be placed with debug mode in a Special Stage.

Seventh Special Stage and its Editor
The seventh Special Stage does not appear in-game by default; it is a custom level that must be created in a special editor and saved before it can be accessed in-game.

To access the editor for this Special Special stage, enter the Stage Select with debug mode enabled, set Max Emeralds to 6 but the Sound Test to 7, and select Special Stage.

The default layout in the editor is nothing but the word "custom" spelled out in generic Special Stage tiles. Upon entering debug mode, you will find three tiles that are not available anywhere else in the game: Load, Save, and Clear icons. You can delete individual objects with the aforementioned prohibitory sign.
 * [[File:Sonic1iOS-load.png]] Load icon - loads your last saved layout for your custom Special Stage when placed. Used in conjunction with the Save icon.
 * [[File:Sonic1iOS-save.png]] Save icon - saves the current layout of your custom Special Stage when placed.
 * [[File:Sonic1iOS-clear.png]] Clear icon - clears your custom Special Stage when placed.

After creating your Special Stage, go to the Level Select and set Max Emeralds to 7. Now your custom stage can be accessed during gameplay (where collecting the Emerald will allow your character to become Super), or by setting the Sound Test value to 7 and selecting Special Stage (helpful if you want to test your Special Stage). In both cases, debug mode will not give you the Load, Save, and Clear icons.

Hidden Credits


The hidden credits are still present. To see them, start a "No Save" game and choose a character. On the SEGA logo screen, tap the letters A-G-E-S in that order once the entire word appears. If done correctly, you will hear the ring chime and the credits will appear.

The credits translate to: Additionally, Tails' name will change to "Miles" during gameplay.

Unused Sprites
Most of these are, unsurprisingly, leftovers from the original Genesis game.

Tails Life Icons from Sonic CD
Leftover Tails life icons from the 2011 Sonic CD port. Found among Tails' sprites.

SCRIPT
No idea, honestly. Probably something related to the Retro SDK's level editor from which the game was built.