Hey, thats great idea, i dont think anyone did that in construct before You. Actually I'm thinking about something like that for a while. I would Suggest that You shouldnt use physics behaviour for particles. It uses too much of computing power, and often is obsolete because You want to simulate very basic and small particles. Personally i think that in this case white 1X1 pixel sprite will be best, and its physical properties should be coded by You. I might do a quick sketch when i got time.