Darkness

Darkness, often referred to shadow as well, is a pivotal element that has played a vital role in The Legend of Zelda franchise. It has served various purposes, both storyline-wise and gameplay-wise, and usually as a manifestation of evil (but not always).

Darkness as a symbolic element
Of all the elemental staples in the series, such as fire, ice or light, darkness has carried over the worst reputation. The reason for this is because this is the signature source of evil in the World of The Legend of Zelda and, most importantly, it's even the origin of the evil beings and creatures that overrun the Light World. Though the line between what is good and what is evil isn't always clear, it is known that there has always been a contrast between light and dark, with Link striving in favor of the former. As detailed above, darkness is frequently portrayed through a setting that is more difficult to conquer than the Light World. Link himself is occasionally forced to fight his dark counterpart as well.

That said, darkness does not always symbolize evil. In Ocarina of Time, aside from the portrayal originated from Ganon and his servants, darkness is canonically represented in the same way the other elements are. That representation, the Shadow Temple, offers several puzzles, obstacles and enemies revolving around it, and is guarded by the Sage of Shadow (by the moment the events of the game take place, Impa fulfills that role, and also guards the Shadow Medallion until she gives it to Link). The Nocturne of Shadow pays homage to the element as well, and instantly transports anyone playing it to the backside of Kakariko Village Graveyard, where the temple is located.

Darkness has been represented by several benign races over the course of the series. One of them is the Sheikah, an extinct race who used to protect the land of Hyrule secretly; the Ikana Kingdom, no longer belonging to the world of mortals, overruns a major region of Termina when the Skull Kid invades the Stone Tower Temple in Majora's Mask; the Twili, formerly the Interlopers in Hyrule, was a peaceful race inhabiting the Twilight Realm until Zant's rise to power; etc.

Darkness as a setting
In addition to the Shadow Dungeons located through Hyrule and several other lands, there are also entire overworld locations that revolve around housing the creatures of darkness. The Dark World, in A Link to the Past, is a notable example, as every location in from the Light World has a geographically direct counterpart in the other setting, havng also a more evil vibe (for example, Village of Outcasts when compared to Kakariko Village). This applies, to a lesser extent, to the landmarks of Hyrule in Twilight Princess when covered by the influence of twilight by Zant and the de-powering of the Light Spirits who guard the different provinces.

In most cases, when Link stands on a place cursed by a dark force, he is affected in one or another way; in the aforementioned examples, the side effect is shapeshifting. In the Temple of the Ocean King, Link loses Sand of Hours continuously when he's not within a safe zone.Dark Fog, also located on dark places, affect the young hero the same way. There may be a higher population of enemies (and some of them being undead) in these places as well.

Darkness as a puzzle device
In some Stealth Missions, such as the infiltration in Deku Palace (Majora's Mask) or in Forsaken Fortress (The Wind Waker), it is convenient to remain in the darkness, and some hunt-based sidequests are best taken place at night.

In Spirit Tracks, some dark rooms house bombable walls that remain unnoticeable if there are lit candles, and Dark Ore must be transported under as little sunlight as possible.