How to Unlock Knuckles's Lava Glasses on Sonic Adventure 2 Battle

Select Knuckles as your character.

Select the "Meteor Herd" stage. You will see a large tower directly in front of you when you start the stage. There is a platform approximately the same height as the starting platform that goes around the tower.

Glide to the tower. Press the "A" button to jump into the air. Continue to hold down the "A" button to glide as Knuckles. You should land or climb up to the platform that goes around the tower. You will begin to climb a wall if you glide into it.

Run along the platform to the other side of the tower. You will see a floating platform with a meteor on it.

Jump onto the platform. You should notice a door on the tower directly in front of the meteor.

Position yourself so the meteor is directly between yourself and the door.

Punch the meteor into the door. Press the "B" button to punch objects as Knuckles. A metal box will appear on the ground in front of the door.

Punch the metal box to destroy it. This will cause the top of the tower to open. You must have acquired Knuckles's Hammer Gloves upgrade in order to destroy metal boxes.

Climb to the top of the tower. You will see lava at the bottom of the tower. There are several floating platforms inside as well.

Jump into the tower. Land on the platform right on top of the lava. You will find Knuckles's sunglasses when you land of the platform.