Sonic the Hedgehog 2 (2013)

Sonic the Hedgehog 2 (2013) is a remastered version of the original Genesis game. It is an HD digital port released for the IOS and Android operating systems simultaneously.

Development
After the success of Christian Whitehead's Sonic CD port in 2011, they immediately started production on reworking Sonic 2 for smartphones. This would mark the first time that Sonic would ever meet the Android phone.

Differences from the original

 * Hidden Palace Zone was included as a scrapped zone that was brought back from being lost in development of Sonic 2. It has an original boss, too. However, Its music remained unused and instead it plays Mystic Cave Zone two player.
 * Knuckles was included in the game without a need for DLC, unlike the original (You had to own Sonic & Knuckles).
 * There's an entirely new Starting Menu and base.
 * The player can now save his/her progress and emeralds. (infinite continues were provided as a result)
 * The player can access a secret sub-menu within the debug menu that allows him/her to use Sonic 3 elemental shields.
 * Tails can now fly and airlift Sonic
 * Special stages are now in 3D rendered environments
 * The game is now at a full 60fps
 * There's a fully remastered soundtrack

Debug mode
It is possible to access the Debug menu by Playing sounds "01, 09, 09, 02, 01, 01, 02, 04" (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 the debug mode. To change the item the player is placing, press the + or - on the top of the screen. Note that tapping the lives counter in Debug Mode will take the player back to the Level Select.

Level select
To access the level select, simply 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, the player will hear the ring chime twice. Then hold two fingers on the bottom of the screen and wait. After the title screen appears, the player'll be taken to the level select.

Game config menu
There is an unused game config menu that can be enabled to replace the more rudimentary menu from the Sonic the Hedgehog (2013). To enable it, play sound 00 three times in the Sound Test to bring up the "Game Config" menu, that includes:
 * Player: Similar to the player select in the Genesis game's options menu, this allows you to play with Knuckles with Tails following, à la the default Sonic and Tails option.
 * Items: Lets you choose between Sonic 2 items, hidden Sonic 2 items (all monitors display a "?" graphic), Sonic 3 items, and hidden Sonic 3 items.
 * Flight: Toggles Tails' signature ability.
 * Air Cap: Toggles the air speed cap.

Eighth special stage
Similar to how Sonic the Hedgehog (2013) added a hidden seventh Special Stage, this port adds an eighth Special Stage. By selecting sounds "00" through 07 in the Sound Test, the player can change which Special Stage the player goes to. Playing sound "00" and selecting Special Stage takes to the Special Stage #1, the first stage takes  to #2, and so on, with #7 taking the player to #8.

The eighth Special Stage layout is purple, a color previously used exclusively in multiplayer Special Stages, and features a corkscrew loop.

Hidden Palace zone prototype


The original Hidden Palace zone is also available in this port of the game, but via the Debug mode. After entering the debug mode cheat, play sounds "03, 03, 03, 0B, 10, 10, 10, 04" and choose "Hidden Palace" on the stage select. As with the stage's original incarnation, it is incomplete and stops at a certain point, although the water slide is now fully-functional. And rather than the "Master Emerald" acting as a breakable object, it instead warps the player back to the Stage Select.

If the player dies in prototype Palace Zone, the player will not be sent back to the level select nor reappear in the Palace Zone. Instead, the game will load the regular Hidden Palace Zone. Completing the stage by placing a goal sign or capsule leads to Oil Ocean Zone.

Egg Gauntlet Zone
The Egg Gauntlet Zone data remains in the final game but can only be accessed through hacking. It was the first attempt at a Boss Attack level that had some original artwork such as mechanical palm trees and flashing lights. It was to be a full Zone that acted as a testing facility for some of the bosses inventions rather than just have a level with bosses back to back. The act was nearly completed and needed just a few graphical changes to replace missing, unpolished, and placeholder graphics. However, Sonic Team did not approve of changing the location, colors, or graphical style so the level was scrapped and the Boss Attack level that was used in the final game was created. As of Version 3.0.9, the Zone was completely removed from the game.

Unused sprites
The list below depicts extracted leftovers from the game, used in the original Genesis game, but did not make it into the digital port gameplay.