""C"", known as "G" (Ｇ Jī for "Gokiburi" (ゴキブリ), meaning "Cockroach") in Japanese, is a series of EARTH Insect Monsters with different Levels whose effects rely on the opponent Special Summoning a monster(s).
The "C" stands for cockroach, and their artworks feature cockroaches (whose eyes are denoted by sparkles) within common household locations that they can inhabit. This is made clear by the sprite used for "Shiny Black "C"" in Yu-Gi-Oh! 5D's World Championship 2010: Reverse of Arcadia. The border of each card artwork also features an ominous-looking, darkened foreground.