Knuckles in Sonic the Hedgehog is a fan-made ROM of the game Sonic the Hedgehog for the Sega Mega Drive/Genesis, featuring the character Knuckles the Echidna in place of Sonic the Hedgehog, the game's usual protagonist. The history of the game begins with the release of the Mega Drive game Sonic & Knuckles. The unique cartridge featured "Lock-On Technology" and allowed players that also owned the game Sonic the Hedgehog 2 to link the two together and play the game through as Knuckles instead of Sonic. However, partly because of a poorly matching colour palette, no such feature was included in the first Sonic game (instead, attaching Sonic 1 to the Sonic & Knuckles cartridge unlocked the full version of Blue Sphere). In the ROM hacking community, creating a patch that allowed the gamer to play as Knuckles in Sonic the Hedgehog was considered the "Holy Grail of ROM Hacking." On September 1, 2005, Stealth created a hack that allowed a player to do just that. His hack was called Knuckles the Echidna in Sonic the Hedgehog (Knuckles in Sonic 1, or S1K for short) Knuckles in Sonic 1 one gives Knuckles all the moves he has in Sonic and Knuckles, including gliding, wall climbing, and the spin dash. Not only that, Knuckles can transform into his Super form once he obtains all the emeralds (a cheat must first be enabled).

Steel Empire (originally released as Koutetsu Teikoku (鋼鉄帝国?) in Japan, and otherwise known in various English materials as The Steel Empire or Empire of Steel) is a side-scrolling shoot 'em up video game released on the Sega Genesis / Mega Drive home consoles in 1992, and was later ported to the Nintendo Game Boy Advance in 2004. Steel Empire is notable amongst shoot 'em up games for its unique aesthetic designs. Mostly low-tech in nature, with its being set in the late-19th century of an alternate world, the game's aircraft, weaponry, powerups, environments, enemies and bosses are heavily stylized adding strong steampunk elements to the style, themes and visuals of the game. Steam power, propeller-based aircraft, biplanes, dirigibles and heavily armored steam trains with giant cannons play large roles in the game's protagonists and opponents. The original leaked Japanese arcade beta version (now rare and the source code of which is believed lost), the popular Mega Drive version and the GBA remake were all critically well received. As of 2012, a modern, "gritty" sequel, Burning Steel, is planned by original HOT・B lead game designer Yoshinori Satake for a 7th generation and possibly an 8th generation console.[