Guest Stars Stephen Stanton voices Sanderson Christopher Swindle voices Phlegm Roberts Gannaway voices Roto Dee Bradley Baker voices Banana Bread Rhys Darby voices Roger Rogers Nathan Fillion voices Johnny Christopher Swindle voices Fungus Bobby Moynihan voices Chet Richard Ayoade voices Declan Alanna Ubach voices Rosie Alanna Ubach voices Maria Paula Pell voices Sunny Janelle James voices Joy Aubrey Plaza voices Claire Romi Dames voices Hazel Julia Butters voices Lorelai Sander Argabrite voices J.J. Christopher Swindle voices Ted Nohely Quiroz voices FearCo. Receptionist Romi Dames voices Addie Dan Molina voices Ethan Max Mittelman voices Kenny Max Mittelman voices Brian Nohely Quiroz voices Adult Monster Rania Sharkawy voices Avani Natalie Lashkari voices Monster Kids