Why the hell is the metal sonic fight so damn hard? I mean for real its damn near impossible to doge any of the attacks when you have two metal sonics attacking you at once. I like the idea don't get me wrong but I keep raging so hard right now. ;(
A metal activates whenever the one you're fighting is almost dead.
Focus on the damaged one and quickly land the two hits needed to destroy it. Do it even if you lose rings.
Do not underestimate your ring buffer: you can get hit repeatedly without dying and you can use it to dispatch the weakened metal rather quickly to bring the battle back into a manageable situation.