The First 15 Minutes of Sonic Mega Collection: Sonic & Knuckles (GameCube)

Copied from MobyGames:

Sonic and Knuckles continues the story directly from where Sonic the Hedgehog 3 left off. The explosion from the Death Egg sends Sonic flying deep into Floating Island's Mushroom Hills. Sonic knows of the Master Emerald hidden somewhere on Floating Island, and is sure that Dr. Robotnik wants it to give his Death Egg limitless power. Knuckles probably knows where it is - but can Sonic stop Robotnik's plans and find the Master Emerald all while fighting off Knuckles?

Sonic & Knuckles is the fourth game in the Sonic series. It retains the same basic features as in the previous Sonic games. Players can select either of the two title characters for play - either Sonic, or the all-new Knuckles the Echidna. Knuckles cannot jump as high as Sonic, but he can glide by holding the jump button while in the air. If you glide into a wall, Knuckles will also be able to climb it. He can also break through walls that Sonic can't. With these abilities, Knuckles can access different areas from Sonic, making for each level an entirely new experience.