So long as it's a creature, Rainbow Star-Serpent has prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Equipped creature gets +2/+2 and has prowess.

Reconfigure {2}{U} ({1}{U}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn’t a creature.)