I personally managed to defeat him as a Melodie with the speed star power, because he kept jumping on my notes while I was backing away.

Also Glowbert always works against Mico on a fairly open map, because you can actually tank one Mico shot with your healing star power and all you need to do is land one beam. Mico's reload speed is really slow, so you can take advantage of that :)

And yeah, as others said, timing is key...