The iOS and Android apps were updated in March 2013 by Sonic community hackers Taxman and Stealth from the ground up, using the Retro Engine also used in the HD remake of Sonic CD (the engine is named after Sonic Retro, a prominent Sonic fansite). Besides featuring a constant 60fps, this remake has a ton of extras, such as the ability to play as Tails, Knuckles and Super Sonic, being able to collect the seventh Chaos Emerald (which allows the player to become the aforementioned Super Sonic), adding Elemental Shields from Sonic 3 & Knuckles, turning on and off the Spike Bug and the ground/air speed caps, and, last but not least, you can add prototype characters and sprites through debug mode, like Splats the Bunny (a Green Hill Zone enemy that never made it into the final game) and the UFOs in Marble Zone.