I'm putting together a Batman Begins/ Dark Knight Scarecrow costume as part of a group cosplay for D*Con this year and since the costume is largely a suit, I think adding a functional Fear Gas tube up the sleeve would really add to the wow factor of the costume. You can see Scarecrow use this weapon about 1 minute in to this video.
Scarecrow- Dark Knight Garage Scene- "Not my diagnosis" - YouTube
So far the best thing I have found is this magician's smoke illusion but I'm worried the smoke won't have the same propelling force as in the film and will just flutter out from under my sleeve.
Pure Smoke by Jason Brumbalow | Ellusionist
Has anyone attempted something similar before and does anyone have advice for alternatives? My major concerns are that it be safe on a convention floor for myself and viewers, compact because it has to fit under a well-fitted suit, economically reasonable, and fit the part of a propelled vapor/ gas weapon. Thanks for any comments!