Guest Stars Christopher Swindle voices Phlegm Alanna Ubach voices Carla Dee Bradley Baker voices Banana Bread Nathan Fillion voices Johnny Joe Lo Truglio voices Jack Ali Wong voices Jill Jenifer Lewis voices Grandma Tuskmon Alanna Ubach voices Maria Alan S. Kim voices Ben Carlos Alazraqui voices Josh Rivera Julia Butters voices Lorelai Aubrey Plaza voices Claire Sander Argabrite voices J.J. Alfred Molina voices Professor Knight Romi Dames voices Lanky Christopher Swindle voices Rudy the Service Monster Carlos Alazraqui voices Jebediah Max Mittelman voices RQR Bro Max Mittelman voices Student Monsters Max Mittelman voices Large Monster Romi Dames voices Student Monsters Nohely Quiroz voices MNN Receptionist Nohely Quiroz voices MU Student Natalie Lashkari voices Little Girl Monster Co Starring Christopher Swindle voices Additional Monsters