Overview

This is a ROM-hack of Knuckles the Echidna in Sonic the Hedgehog 2 (yes, that mouthful really is its name) that restores various removed features from Sonic the Hedgehog 2. In particular, it restores the ability to play as Sonic and Tails, as well as two player mode.

Knuckles in Sonic 2 includes a number of tweaks and bugfixes (such as reduced Special Stage difficulty and the removal of Sonic 1's leftover air speed cap) that make it akin to an updated revision of Sonic 2, but its lack of essential features, such as being able to play as Sonic and Tails, hold it back from being the original definitive version of the game. This hack aims to address that, allowing the player to experience the 'Sonic 2 & Knuckles' that could have been!

Technical Background

One tool that is practically a requirement for ROM-hacking is a good disassembly, and this is something that Knuckles in Sonic 2 lacked for the longest time. Back in 2022, however, that changed when I made my own disassembly. It was created by taking the existing Sonic 2 disassembly and editing it until the ROM that it produced matched that of Knuckles in Sonic 2. This avoided the fragmentation and duplicate effort of creating a separate disassembly from scratch.

Due to the method with which the disassembly was produced, I was able to record each and every change that the original developers made to Sonic 2 to create Knuckles in Sonic 2. Not only was this useful for discovering long-hidden bugfixes, but it also provided an exact list of changes that were responsible for removing several features, such as two-player mode, the options menu, Sonic, and Tails. All I'd have to do is undo those modifications, and all of these features would be restored!

Usage

This ROM-hack is made available in three formats:

• 'upmem.bin' - Must be attached to a combined Sonic & Knuckles and Sonic 2 ROM, just like the regular Knuckles in Sonic 2 does.
• 'combined.bin' - A pre-combined Sonic & Knuckles, Sonic 2, and 'upmem.bin' ROM.
• 'standalone.bin' - A regular Mega Drive ROM.

The standalone version of the ROM removes the Lock-On Technology logic. It is intended for flash cartridges and emulators that have compatibility issues with Knuckles in Sonic 2, such as the Everdrive MD v3.