Warlock Utility 16Cloak of Shadow
You briefly become a flying shadow, swift and insubstantial.
Move Action Personal
Effect: Fly a number of squares equal to your speed + 2. If you don’t land at the end of this move, you fall. Until the end of your next turn, you are insubstantial, and you cannot affect, attack, or use powers on creatures or objects.
Published in Player's Handbook, page(s) 137, Class Compendium.