Metal Sonic in Sonic 3 & Knuckles replaces Sonic with Metal Sonic from Sonic CD, you can no longer choose from the numerous playstyles but Metal has his own abilities such as use of the elemental sheilds and a boost. Metal Sonic must save Angel Island and take down his Mechanical Doppleganger.
Metal Sonic in Sonic the Hedgehog 2 swaps Sonic out for Metal Sonic from Sonic CD, you can choose between the Original moveset, Sonic CD, or the 2011 remaster moveset from Christian Whitehead's port of Sonic CD Metal will once show Robotnik he's not a bot to be forgotten...
Platform / Action / Science fiction
Metal Sonic Hyperdrive is a modification of Sonic the Hedgehog that stars Metal Sonic as the main character role - more specifically a reprogrammed Metal Sonic. The hack also features other characters besides Metal such as: Sonic,Lone Devil (KAZ),Kirby, and even Somari! Each coming with their own unique abilities: Metal can use the Super Peel-Out, and Maximum Hyperdrive Attacks, Sonic can Spindash in traditional fashion. Somari can spindash, but in a less traditional fasion, Lone Devil can use his Sythe to attack and freefall, and Kirby can inhale enemies, no copy abilities.
Knuckles' Emerald Hunt is a modification of Sonic the Hedgehog 2 that split off from another hack Sonic 2 Adventure Edition. It's main goal is to mimic the Emerald Hunting Gameplay from Sonic Adventure 2/Battle. Playable characters being Knuckles and Tikal, through each stage you must find and collect 3 Emeralds or Emerald pieces. The Game features the radar from SA2, and a secret Sandwich mode in which all the emeralds are replaced with Sub sandwiches and the Master emerald is replaced with a Subway footlong. It also features the Scrapped Hidden Palace Zone and some Sonic 1 Zones
Crazy the Hedgehog is a modification of Sonic the Hedgehog for the Sega Genisis, in which you play as an alternate dimension version of Sonic named Crazy. Crazy has to defeat the parallel of Dr. Robotnik, Dr. Mechanik and his robot army as he's attacking North Island, to find the Dimensional Gems! But this dimension isn't exactly like it's parallel, it's similar but different, its a crazy world! This hack features new level palettes and layouts.
Big's Fishing Derby is a total-conversion modification of Sonic the Hedgehog 2, based on Big's Fishing mini game in Sonic Adventure, the same premise applies. Big must catch froggy to obtain the emerald he swallowed, Dr. Robotnik also is fishing for froggy to obtain all the Chaos emeralds! Big must protect froggy and keep the emeralds out of Robotnik's hands!
Amy in Sonic 1 is a modification of Sonic 1 that swaps sonic out with Amy Rose from Sonic CD, bringing with her, her move-set from Sonic Advance. Using Her Piko Piko Hammer she will have to Jump, whirl, and dash through South Island to put a Stop to Robotnik's plans.
Tails and Charmy are the flying types with the ability to soar through the air nothing stands in their way, and with Each carrying a legion of friends when super or hyper, Dr. Robotnik's forces don't stand a chance! Knuckles and Vector are the power types delivering devistating blows to Robotnik's Badnick army combine that with the ability to Glide, climb walls, and Power Dash, these two are the roughest, toughest dudes around. As if the Teams weren't enough to sway you new powerups make their rounds aswell: Home in on Robotnik's forces with the Homing Sheild, Burn those bots with a fire sheild. Short-circuit them with an electric sheild, If a watery grave awaits you a bubble sheild is just around the corner. The Sol Emeralds have also managed to cross dimensions through the Special Zone but not to worry Team Sonic and Chaotix are on the job! Using both the Power of the Chaos and Sol Emeralds will unlock a very familiar power.... can you collect all 14?
Amy Rose in Sonic the Hedgehog 2 swaps Sonic out for Amy Rose from Sonic CD, equipped with her Sonic Advance moveset. She will have to Jump whirl and Dash through Westside Island with the help of her newfound friend Tails! Infiltrate the Death Egg and put a stop to the deadly Space Station using your hammer!