Dry Ice in the mask, just for some fancy white smoke?
Think twice about it, while it sounds good, this is your problem:
First it freezes the moisture on and near the surface of your skin, causing your skin to 'stick' to the dry ice. It then freezes the cells on the outer layers of skin, bursting their cell walls and killing the cells. it keeps penetrating deeper until it reaches a depth where the blood supply can provide enough heat to supply what is being conducted away. The direct result is frostbite. The eventual result, if left untreated, is usually gangrene. If the gangrenous tissue is cut away, sometimes requiring amputation of the limb, you survive. Otherwise the normal result is death from gangrene.
I would route a mini fog machine from your belt, up the back of your cloak through the hood and into the mask with surgical tubing. You can buy it at most hardware stores.
Why risk a health issue over what could be a lame effect to begin with.
No intent on being a jerk, Ive messed around my fair share with dry ice and seen some bad stuff.