Fog

The Fog is a trap that can curse Link if he comes into contact with it in and Twilight Princess.

Blue Fog
A billowing Blue Fog can be found in certain areas of the Earth Temple. If Link comes into contact with it, he will become jinxed, meaning that none of his items work, including his sword. While affected, Link is surrounded by a concentrated smog, his body flashes purple, and he acts disoriented or weakened. This is markedly similar to being cursed by a Blue Bubble. The curse will not be lifted unless he gets out of the fog or finds a beam of light to take refuge under.

To get through the foggy areas safely, Link can use the Deku Leaf to blow the fog away from a small area at a time, and if he shines light at it with his Mirror Shield, the part of the fog exposed to the light will dissipate. Medli can also use the face of her lyre in the same fashion. The pair will often have to work together to travel through, or over, the fog unhindered.

Dark Fog
Dark Fog is an element that is found only in the Palace of Twilight, the eighth dungeon in Twilight Princess. This mysterious haze-like element is comprised of Shadow Crystals created by Zant's wicked magic. It is scattered across various parts of the Palace, and if Link comes in contact with the mysterious element, he will transform into his wolf form, and will be unable to have Midna transform him back into his human shape until he leaves the fog or clears it. Once Link obtains the light-infused Master Sword, he will be able to clear away Dark Fog using the Spin Attack. Midna mentions that the Dark Fog is what caused Link to become a wolf in the beginning of the game.