Sandopolis Zone

Here's where the game starts to get good. The first act is outside. Little sandfalls should allow Sonic or Knuckles to progress up them by jumping, others will automatically be run up. The loops here are different, because when you go through one, you will go around and around, then it launches you high into the air. The mini-boss is a rock golem that highly resembles the Egg Golem from Sonic Adventure 2: Battle. All you have to do is lead it to the sand flow and have it jump in. The second act takes place inside a pyramid. The gimmicks here are a plenty. The light in the pyramid must be on or else you will get attacked by ghosts. There are switches in the pyramid that open doors but you must be quick about it. Also, there are bricks that hold sand flows that will help you get higher in the pyramid, but it can crush you beneath the roof if you are not quick enough. The boss is another reference to the Egg Golem. You need to attack the head so that it reveals Eggman, then attack him. After you defeat him, release the animals to proceed to Lava Reef.

Trivia

 * The entrance to Lava Reef is different between Sonic and Knuckles. Sonic goes into a tunnel, but falls through a hole, but Knuckles runs right over it, even though the pre-released ghosts should indicate that Sonic has been there first, and Knuckles should fall to because the hole is already open.