Alfred Molina

Professor Knight (voice)

Aisha Tyler

Millie (voice)

Stephen Stanton

Smitty / Needleman (voice)

Dee Bradley Baker

Banana Bread (voice)

Alanna Ubach

Cutter / Maria / Carla (voice)

Nathan Fillion

Johnny (voice)

Jenifer Lewis

Grandma Tuskmon (voice)

Ali Wong

Jill (voice)

Joe Lo Truglio

Jack (voice)

John Ratzenberger

Bernard (voice)

Christopher Swindle

Phlegm / Rudy / Additional Monsters (voice)

Roxana Ortega

Celia Mae (voice)

Alan Kim

Ben (voice)

Aubrey Plaza

Claire (voice)

Julia Butters

Lorelei (voice)

Sander Argabrite

J.J. (voice)

Nohely Quiroz

MNN Receptionist / MU Student (voice)

Natalie Lashkari

Little Girl Monster (voice)

Max Mittelman

RΩR Bro / Large Monster / Student Monsters (voice)

Carlos Alazraqui

Josh Rivera / Jebediah (voice)

Romi Dames

Lanky / Student Monsters (voice)

Kimberly Brooks

Additional Monsters (voice)

Billy Crystal

Mike (voice)

John Goodman

Sulley (voice)

Ben Feldman

Tylor (voice)

Mindy Kaling

Val (voice)

Henry Winkler

Fritz (voice)

Lucas Neff

Duncan (voice)