Keegan-Michael Key

Buddy the Unicorn (voice)

Cristin Milioti

Grace

Delaney Quinn

Freddy

Caleb Williams

Wade

Madison Polan

Hannah

Tristan Borders

Oliver

Patton Oswalt

Strappy (voice)

Jimmica Collins

Betty Bunny (voice)

Eric Bauza

Mr. Mailbox / Worry Well / Couchy / Trashy / Pee Flower (voice)

Topher Grace

Ben

Bryson JonSteele

Derek

Seamus Flynn

Timothy

Luke Speakman

Josh

Bennie Taylor

Mailman Miles

Phuong Kubacki

Nurse Nancy

Devon Hawkes Ludlow

Charlie the Train (voice)

Michael Shannon

Willie (voice)

Clint Howard

George

Sergey Zhuravsky

Buddy the Unicorn (suit)

Jonathan Yurco

Dark Buddy (suit)

Cedwan Hooks

Betty Bunny (suit)

Mark Aaron Buerkle

Therapist (Day Player)

Conner Stumm

Mailman Justin

Eric Salazar

Grilling Man

Lynette Eklund

Puppeteer

Tory J. Malone

Tyler

Brooke Bloom

Dr. Deborah Burr

Rachel Appelbaum

Clocky / Mr. Mailbox (uncredited)

Frank Brown Jr.

Father (uncredited)