"Stygian", known as "Hell" in OCG, is a series of DARK Fiend monsters. They are used by Trudge in the Yu-Gi-Oh! 5D's anime. They are named after the river that people had to be ferried across by Charon in Greek mythology, the River Styx. They resemble demonic police officers.
"Samurai Sword Baron", "Stygian Sergeants" and "Stygian Security" were released as promotional cards with Yu-Gi-Oh! 5D's World Championship 2010: Reverse of Arcadia. "Stygian Street Patrol" was released as a promotional card with the game guide in the OCG, while it was released as part of the Duelist Revolution set in the TCG.