Guest Stars Walton Goggins voices Cecil Stedman Zazie Beetz voices Amber Bennett Gillian Jacobs voices Samantha Eve Wilkins / Atom Eve Andrew Rannells voices William Clockwell Jason Mantzoukas voices Rex Sloan / Rex Splode Grey DeLisle Griffin voices Amanda / Monster Girl Chris Diamantopoulos voices Donald Ferguson 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