Another regular from Starz's "Spartacus" is joining the cast of "Arrow" as a villain. Nick Tarabay has scored the recurring role of Digger Harkness, better known as DC villain Captain Boomerang, in the upcoming third season of the series. In the show, he will be an ex-ARGUS operative skilled in martial arts and espionage, with a thirst for vengeance against his former employers.