Sonic 3D and Knuckles is a 2D side-scrolling game. It is a remake of Sonic 3 & Knuckles.
Sonic the Hedgehog
In Sonic's story, after discovering Angel Island, the Island's guardian, suprises the blue hedgehog and causes Sonic to lose his Super form. While Sonic is still dazed, Knuckles steals the Emeralds an, Sonic jumps off Tornado and turns Super Sonic and arrives on the Island. Once there, Knucklesd hides them in the Special Stage. It's up to stop Sonic Eggman and get the Master Emerald and the Chaos Emeralds plus the Super Emeralds and save the world.
Knuckles the Echidna
Knuckles' story takes place where Sonic's story ends. After Robotnik's defeat, Mecha Sonic and EggRobo staged a last-ditch effort to steal the Master Emerald again. They start by stealing the Master Emerald while Knuckles' back was turned at the end of Sonic's story. After progressing through the Floating Island in the same order Sonic did previously, he is taken by EggRobo to Sky Sanctuary, Mecha Sonic then accidentally attacks the EggRobo and fights Knuckles. After losing to the echidna, Mecha Sonic flees and absorbs the power of the Master Emerald and becomes Super Mecha Sonic. Knuckles defeats him nonetheless, and the platform Knuckles was on gives way and luckily, Sonic saves him and takes him back to Angel Island where it's power is fully restored once again.
Metal Sonic is the last character in the game, and can be unlocked by beating the special ending in Sonic's story based on the final level in Sonic CD. Metal Sonic's story also takes place after Sonic's story, after Sonic deafeted Metal Sonic, he got his electronics had been damaged by Sonic's fur. The fur then changes Metal Sonic's DNA had changed to Sonic's DNA. He then escapes the Death Egg then goes on to destroy Eggman's plan.
- This is the only Sonic the Hedgehog game where Tails isn't playable nor in.
- This game is the first Sonic the Hedgehog where Metal Sonic is a playable character.
- This game is a remake of Sonic 3 & Knuckles.