While following the current storyline and hearing input from the community, one issue commonly brought up is Umarak's ineptitude at capturing the Creatures, even after thousands of years. This theory, if true, may explain why that is, and why forging a mask of more than one element is so dangerous. Umarak came into being when the Creatures did, to balance the six elements with the darkness, or shadow. The reason he never caught them was because of this balance; in an almost yin yang fashion, neither the creatures nor Umarak could gain the upper hand, because the creatures were united against him, and the island's elements were in harmony. However, when Makuta made the MoUP, he upset the balance, and due to this upset in balance the island degraded, and the Creatures were divided, drawn to the areas where their element was the most prominent, to resume an uneasy game of cat and mouse with Umarak for years afterwards. However, while Ekimu did stop Makuta from further destabilizing the island, that initial destabilization did give Umarak an advantage. Shadow and Destruction, in my opinion in regards to this story, is that combination of elements forcibly wielded by one, while Creation and Life are represented by the individual elements each wielded by one, working together. Therefore, the existence of the MoUP slowly began to change the nature of Okoto, causing the natives to more heavily modify their regions to suit one element, which made the unity of elements on Okoto much weaker against the united forces of darkness. This, in turn, led to the eventual arrival of the Toa, to "balance the elements and shadow" again. But the unforeseen consequence of that was Umarak, the only fully alive user of shadow, gaining more power, to balance the power of the Toa AND Creatures, and this is why it is so important that the Toa and Creatures unite, so they can stand a chance against the shadow. Additionally, the Toa's arrival probably also boosted the abilities of Makuta, who is the only other known being in the Okotoverse that utilizes the shadow, and functions as a counterbalance. Well, that was a longer post than expected! In short, I think that the shadow element in this universe is a combination of the elements used by one, while the protagonists each wield one element, working together to balance the darkness. One quick correction: It is my opinion that Life or Light is represented by numerous beings working together, and this is the only way great power can be wielded for the good; Unity of the users, Duty to those they protect, and their Destiny on the horizon.