It's alot simplier that all the mechanics and gas cannisters, We have monster breathing "smoke" at the haunted house.
Take a small plastic bottle, drill a hole in the top and bottom.
Now fill the bottle with baby powder
Take 2 really small hoses, insert one in the top and one in the bottom.
Seal around the hoses if you need to ( hot glue )
One of the hoses runs down your arm to your finger tip or wrist, the other up you mask to your mouth. ( we mount ours in the mask, so it's not always in your mouth but is quickly gotten at)
Breath out...a great puff of "smokey mist" fills the air...
best part is it costs about $2. to make
I was actually going to make a scarecrow costume in the future and I'm going to use this method.
Mike