Form of the Shadowy Spectre
MuCo45(Ig)
With this spell the caster seems to sink down into his own shadow which thickens and takes on a more defined form. While in shadow form the caster is immune to physical damage but takes damage from sunlight as if it were fire. Fire also does +5 damage to the caster in this form making it unwise to use at a Flambeau party. The nature of the shadowy form allows it to slip through narrow cracks such as door jams and through see through materials such as water and glass as if they weren’t there. The caster holds a piece of glass with him and symbolically breaks this to return to his human form.
(base 30, +1 complexity, +2 sun)
Comments/corrections welcome 
Sounds good to me.
And ouch, so expensive!
This sort of a comment may be on the other shadow magic thread that I see up on the board but I think of shadow as imagonem rather than ignem thus I'd make this a muto imagonem spell. (Not that I've seen anything in the rules to specifically define it in one way or the other.)
I'd also decide how much sunlight compares to how hot of a fire (ie. is high noon on a cloudless summer day +15 per round? +20? +10?)
Like it was mentioned, check out the PeIm sidebar:
pg 146: "Note also that shadows are due to the physical body blocking the light. Destroying something's shadow is thus Creo Ignem, or possibly Rego Ignem, not Perdo Imaginem."
Shadows, in Hermetic theory, are all about the ignem. I can see where you're coming from, but it also makes sense to make them ignem, since ignem deals with light. For ArM5, shadows are absence of light, light is ignem.
-Ben.
I disagree. Consider two slabs rising from the ground in mid-morning. One of them casts a shadow; that is, light (ignem) isn't getting to a certain area, because the slab is blocking it. We've set up artificial lighting for the other one, so it isn't casting a shadow. However, we've also painted the ground the exact color that a shadow would have made; i.e., black.
The shadow is black because of an absence of light. There's no light to carry visible species, so you can't see anything. The painted area is not black because of an absence of light. There's plenty of light to carry visible species; there's just no species. In both cases, no visible species are transmitted, but for different reasons. The shadow's blackness has nothing to do with imaginem, but only with ignem.