The combo attack is a technique where both Sonic and Knuckles combine their powers. When using it, Sonic and Knuckles grab each other's hand and begin spinning around in mid-air until they form a rather large blue and red-colored Spin Attack enveloped in a circular wave of wind/jet stream created by the spin's speed, with each participant using a synchronized Spin Attack inside it. While using this attack, Sonic and Knuckles are turned into a powerful projectile that can pierce through lasers and solid objects which neither Sonic or Knuckles can penetrate separately. It also allows limited flight, like a boomerang.
The combo attack was suggested by Sonic to Knuckles in order combine their strengths to intercept the Egg Battleship's death ray before it could be fired. The attack was successful and took the entire ship down.