Become Shadow

Your body dissolves into a cloud of black smoke, and for the duration you only exist as a shadow on this plane of existence, temporarily in the space between your current plane and a harmless demiplane. While affected by this spell, you can see and hear the plane you originated from, which is cast in shades of grey. No creature can affect or be affected by you unless they also exist in this space between planes, however you are visible in your original plane as a shadowy silhouette.  Your movement speed increases by 10 feet, you are unaffected by difficult terrain, and you do not provoke opportunity attacks. When the spell ends, or you end it using a bonus action, you materialize fully into your original plane. This spell does not allow you to pass through solid objects or other creatures. 

At Higher Levels. When casting this spell using a higher spell slot, the duration of the spell increases: 10 minutes at 5th level, and 1 hour at 7th level