"Darkness" (ダークネス Dākunesu) is an archetype of cards used by Nightshroud (whose own Japanese name is also "Darkness") in the Yu-Gi-Oh! GX anime. In the OCG, the archetype is exclusively supported by Boss Duel cards.
So far, the only "Darkness" monsters used by Nightshroud that have been released in the OCG or TCG (excluding Boss Duel cards) are "Darkness Destroyer", "Darkness Neosphere", "Red-Eyes Darkness Dragon" and "Red-Eyes Darkness Metal Dragon", although other cards can be supported by the anime-only support cards.
"Red-Eyes Darkness Dragon" appears as a character in World Championship 2006, and in World Championship 2007, "Light and Darkness Dragon" appears in World Championship 2009, "Darkness Neosphere" appears in World Championship 2010, and "Red-Eyes Darkness Metal Dragon" appears in World Championship 2011.