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 Chris Diamantopoulos voices Donald Ferguson Grey DeLisle Griffin voices Amanda / Monster Girl Khary Payton voices Black Samson Ross Marquand voices The Immortal Ross Marquand voices Rudolph "Rudy" Conners Seth Rogen voices Allen the Alien Jay Pharoah voices Zandale Randolph / Bulletproof Mark Hamill voices Art Rosenbaum Sterling K. Brown voices Angstrom Levy Clancy Brown voices General Kregg Ben Schwartz voices Shapesmith Luke Macfarlane voices Rick Calista Flockhart voices April Howsam Ben Schwartz voices Rus Livingston Scoot McNairy voices King Lizard Lincoln Bodin voices Oliver Grayson Ross Marquand voices Proprietor Chris Diamantopoulos voices GDA Med Tech Grey DeLisle Griffin voices Helga Grey DeLisle Griffin voices Nurse Khary Payton voices Martian Leader Ben Schwartz voices Tech Trooper #2 Kevin Michael Richardson voices Tech Trooper #1 Kevin Michael Richardson voices Monster Co Starring Nyima Funk voices Additional Voices Ami Shukla voices Additional Voices Robert Kesselman voices Additional Voices Dan Navarro voices Additional Voices