I'm probably about as confused as DNA is right about now.
What exactly is your question here specifically?
The way you stated it in the first post, you said Magnezone uses its Gyro Ball attack against a Defending Pokemon that has Rocky Helmet attached. That means that the Defending Pokemon is Active, takes the damage from Gyro Ball, and then the two damage counters are applied to Magnezone before the Defending Pokemon _and_ Magnezone goes to the Bench. Now if you have a separate question to that scenario, you need to explain it in detail.
dmaster out.