The game’s 2nd main bad guy, Infinite challenges the player early on in the game. We first think we’re going to fight him perhaps as Silver the Hedgehog.
But Sonic saves his friend at the last moment.
So you play as Sonic for the whole boss battle. You run on a big pillar thing while jumping over some magic by the Phantom Ruby.
Before getting a chance to cause Infinite some damage. While a decent boss battle, it could have been better.
But you don’t defeat him for good, he runs away before Sonic could land a mortal wound.