Guest Stars Walton Goggins voices Cecil Stedman Zazie Beetz voices Amber Bennett Gillian Jacobs voices Samantha Eve Wilkins / Atom Eve Jason Mantzoukas voices Rex Sloan / Rex Splode Andrew Rannells voices William Clockwell Grey DeLisle Griffin voices Amanda / Monster Girl Zachary Quinto voices Robot Khary Payton voices Black Samson Melise voices Kate Cha / Dupli-Kate Ross Marquand voices The Immortal Ross Marquand voices Rudolph "Rudy" Conners Grey DeLisle Griffin voices Shrinking Rae Kevin Michael Richardson voices Mauler Twins Seth Rogen voices Allen the Alien Mark Hamill voices Art Rosenbaum Gary Anthony Williams voices GDA Scientist