If I use a pluspower on a Clefairy/Clefable and use metronome does the attack add a damage. I was wondering because it isnt metronome that does the damage, is it?

Metronome copies an attack, and PlusPower adds damage to that attack.  So, yes - If I Metronome Hitmonchan's Special Punch with a PlusPower, it will do 50, not 40.

Scott