Dark Mist is a kind of black fog that usually appears when Dark Techniques are used by some of the important antagonists like Kabazu, and Shirazu.
When it apppears[]
Dark Mist appears around the user fo a Dark Technique or sometimes around the technique. Normally, it is intangible and cannot be felt, but is just a sign of darkness. The only two people which have had the Dark Mist around them are Kabazu, Shirazu, and Daremadu. The creatures that are "Dark Cursed" usually have Dark Mist around them.
Battle Usage[]
Dark Mist is normally intangible and cannot be felt, only seen. Shirazu, hower, had the ability to touch opponents with the Dark Mist around him, usually choking them. Shirazu has also made a special technique using Dark Mist which is called the Dareganque Dragon Bite. Since Shirazu learned Dark Techniques from Kabazu, whose spirit still remained on earth after he got destroyed by Kochishimaru, it is likely that Kabazu can also control Dark Mist and use them for battle, and be the one who actually created the Dareganque Dragon Bite.