The green and blue spark sprites were supposedly made for units to use when shooting bullets or lasers. Instead, the unit death sprite was used. Laser weapons are generated in code by the game and have no actual sprites. The nuke explosion is a complex movie that plays when a nuke is fired (it uses the giant grey scorch and white blast to accomplish a convincing nuke explosion). The orange spark is used under miners when they are gathering crystals (it uses special effects to fade in and out and flip horizontally and vertically). The asteroid is used in a minigame on startup as you wait for the game to load all the assets it needs to function.