Sonic the Hedgehog

To get a chaos emerald, you have to get to a special stage. In order to get to a special stage you must have at least 50 rings with you upon completion of an act. At the end of the act when you pass the post, a giant ring will be there and you must jump into it. Do so quickly because after passing the finish post, you have only a few seconds to get into that ring. It's also possible to miss the giant ring if you sprint pass the post and go off screen. The game will not let you go back on screen to jump into the giant ring.

Once you go to the special stage SAVE!!!! If you screw up you miss your opportunity to get the chaos emerald. You fail the stage by hitting bright red flashing circles. Reload your game and start over. Save after you get it.