Special Zone entrance: You can almost always have the Special Zone entrance open (the giant ring next to the sign at the end of level Acts 1 and 2) by not losing your rings. If you do lose your rings, when you pass a checkpoint, intentionally die, then continue through the level without losing any rings. This works about 80% of the time.

Easy Emeralds: Enable the "Debug mode" code. At the beginning of the level, create 50 rings and have Sonic collect them. Then, take Sonic to the end of the stage where you the giant ring. In the special stage, turn Sonic into an item and bring him to the end of the stage where the emerald is located. Turn him back and he will immediately get the Emerald. Repeat this until you have all six.