Sonic the Hedgehog (2013)

The 2013 re-release of Sonic the Hedgehog is a remastered downloadable remake of the original Sonic the Hedgehog for the Sega Mega Driveon the iOS and Android mobile platforms. It was released on 15 May 2013 for iOS and on 16 May 2013 for Android. The iOS is also a free update to those who purchased the earlier iOS port of the game. It was developed by Christian Whitehead and Headcannon using the Retro Engine, the same game engine used for the 2011 re-release of Sonic the Hedgehog CD.

Gameplay
The gameplay remains generally faithful to the original Sonic the Hedgehog but it runs at 60 FPS, has widescreen support and a remastered soundtrack. In addition, the game has received new features and gameplay changes

New features

 * The Spin Dash is now included as an optional move.
 * Despite not being officially introduced yet in the series, Miles "Tails" Prower and Knuckles the Echidna are unlockable characters, with mild tweaks to the level design to accommodate their gameplay. They both retain the same movesets they had in Sonic the Hedgehog 3 & Knuckles. Tails can also accompany Sonic like he did in Sonic the Hedgehog 2 and Sonic the Hedgehog 3 & Knuckles.
 * Tails is unlocked by completing the game once while Knuckles is completed by completing the game with all six Chaos Emeralds.
 * A hidden seventh Chaos Emerald and Special Stage was included via Level Select.
 * As such, super transformations of Sonic, Tails and Knuckles are also enabled.
 * A Time Attack mode is included.
 * The hidden Level Select and Debug Mode options are greatly expanded, taking elements from the sequels as well as incorporating recreations of unused content.

Changes

 * The title screen now changes based on the player's characters. As such, it can alternatively display Miles "Tails" Prower in Sonic the Hedgehog (for Tails alone), Sonic the Hedgehog and Tails (for Sonic and Tails) or Knuckles the Echidna in Sonic the Hedgehog.
 * Level layouts were tweaked to accommodate the gameplay of Tails and Knuckles.
 * Spikes on the wall and Rings in the air that can only be reached by Tails or Knuckles have been added above the Lamppost between the two S-tunnels near the end of Act 1.
 * The boss of Green Hill Zone has a wider arena and also, Dr. Robotnik can no longer be prematurely attacked until the wrecking ball has been fully deployed.