The First 15 Minutes of Sonic Mega Collection: Sonic The Hedgehog 2 (GameCube)

Copied from MobyGames:

Sonic the Hedgehog 2 is a side-scrolling platformer based around speed, and the sequel to Sonic the Hedgehog. The evil Dr. Robotnik wants to conquer the world. In order to do that, he imprisons and transforms all animals into robots called "Badniks". This way they can build his powerful weapon, the Death Egg. Only Sonic the Hedgehog, and his new tagalong partner, Miles 'Tails' Prower, can stop Robotnik and his army of Badniks from taking over the world.

Sonic and Tails can collect rings which are scattered throughout all of the levels. As with most platformers, when the player collects 100 rings, they earn an extra life. However, the rings also act as protection; if Sonic is hurt when he is carrying rings, they scatter everywhere and he is briefly invincible. If he is hit again when he has no rings, he'll lose a life. If the player reaches a continue point lamppost with 50 or more rings, they'll be able to access the Special Stage. In this stage, you must gather a set amount of rings in a halfpipe-like stage before you reach a checkpoint. Complete all the checkpoints and you'll earn one of the seven Chaos Emeralds.