You fly apart into a swarm of batlike shadows.

Daily   ✦     Arcane, Polymorph
Minor Action      Personal

Effect: You assume a shadowy form until the end of the encounter or for 5 minutes. In this form you are insubstantial, gain fly 6, and can't take standard actions. Reverting to your normal form is a minor action.

Published in Player's Handbook, page(s) 136, Class Compendium.