Co2 is used in the creation of heavy, low-lying fog. This effect requires a specific cold flow system, which allows the liquid fog to remain dense and low before evaporating. Co2 tanks are used to cool the smoke before it's ejected from the nozzle of the box. Many times, live performances use this effect for ballads or more serious, slow songs. On a smaller scale, dry ice, Co2's solid form, can be used to create a low-lying fog.
Co2 is also used in the effect of gigantic plumes of what appear to be smoke. In actuality however, the plumes are just Co2 vapor being propelled out of a tank by compressed air (which also happens to be Co2). Depending on the timing of the effect, you can have rapid bursts of "smoke" columns, or a continuous stream of "smoke." If you opt for the continuous stream, adding lights to the dense fog will create an even more dramatic effect.
If you're able to obtain a Co2 cannon, you can use small tanks of Co2 to launch confetti, glitter or streamers with the touch of a button. There are single barrel and mutli-barrel cannons available, allowing the user to initiate multiple effects simultaneously. Most Co2 cannons take pre-loaded tanks for easy installation and disposal.