Guest Stars Stephen Stanton voices Sanderson Roberts Gannaway voices Roto Christopher Swindle voices Phlegm 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 Janelle James voices Joy Paula Pell voices Sunny Aubrey Plaza voices Claire Julia Butters voices Lorelai Romi Dames voices Hazel Sander Argabrite voices J.J. Christopher Swindle voices Ted Nohely Quiroz voices FearCo. Receptionist Max Mittelman voices Kenny Max Mittelman voices Brian Romi Dames voices Addie Dan Molina voices Ethan Nohely Quiroz voices Adult Monster Rania Sharkawy voices Avani Natalie Lashkari voices Monster Kids