John Krasinski Marshmallow Director, Actor, Screenwriter, Producer Cailey Fleming Bea Actor Ryan Reynolds Cal Actor, Producer Fiona Shaw Grandmother Actor Phoebe Waller-Bridge Blossom Voice Louis Gossett Jr. Lewis Voice Steve Carell Blue Voice Alan Kim Benjamin Voice Liza Colón-Zayas Janet Actor George Clooney Spaceman Voice Bradley Cooper Ice Voice Matt Damon Flower Voice Emily Blunt Unicorn Voice Maya Rudolph Alligator Voice Jon Stewart Robot Voice Keegan-Michael Key Slime Voice Bobby Moynihan Jeremy Actor Sam Rockwell Guardian Dog Voice Sebastian Maniscalco Magician Mouse Voice Christopher Meloni Cosmo Voice Richard Jenkins Art Teacher Voice Awkwafina Bubble Voice Matthew Rhys Ghost Voice Amy Schumer Gummy Bear Voice Bill Hader Banana Voice Blake Lively Octopuss Voice Allyson Seeger Producer Andrew Form Producer