According to a persistent myth, the Mask of Creation was the Kanohi mask worn by Artakha. The mask helped its user to envision how things should look and be designed; it did not actually bring things into being. Only one Mask of Creation existed. According to legend, Artakha and Karzahni competed for the right to wear the mask, and Karzahni lost.1
Notes
If the rumored Mask of Creation existed, it would be a legendary Kanohi.2 This does not denote its power level, it solely means the mask exists in legends and it's unknown if it exists in reality.3
It was possible to lose control of the Mask of Creation. Greg Farshtey compared this situation to the plot of the movie Forbidden Planet, in which one's dangerous subconscious thoughts are made real.4