Sonic Adventure 2 (Battle) Upgrade Guide-Aquatic Mine (Air Necklace)
Character-Knuckles the Echidna
Required Upgrades-N/A
Next to the Sunglasses, this is the most commonly missed upgrade for Knuckles so you may wanna pay attention, it comes EXTREMELY in handy in Cannon's Core! Collecting this upgrade will take away the air timer, allowing you to stay underwater as long as you like!