I beat Earthbound.
SPOILERLOL
I always expected Pokey to be the villan, and he was: Sadly due to the total obliteration of all the evil in his heart Ness could not actually kill Pokey and thus Pokey is the main enemy in M3.
I also love how singing to Giguge in EB0 owns him: I mean, really.
"Oh god the situation's getting hopeless! This means I must sing!"
"Ooh, you're singing? Lemme sing too!"
"Yaaay, Singing!"
"Osh-"
"Take a melody..."
"AGH, MY BEJEEBUS!"
"Hey, that had an effect! We must sing more!"
"Yay!"
"Yay!"
"ONO"
(8 more turns of the song later)
"MY VITALS"
"We defeated an ultimate evil alien of death by singing! Yay!"
"How anticlimactic."
I think they reflected that in M3 by having Lucas and Co. be able to score additional attacks by bashing along to the rhythm of the song. For instance smacking an enemy once would do X damage, but than getting a full Rhythm Combo you'd deal twice that!
"OH CRAP IT'S THE ULTIMATE CHIMERA!"
"Rawr"
"We must SING!"
"Rawrosh-"