Cristin Milioti
— Grace
Delaney Quinn
— Freddy
Topher Grace
— Ben
Keegan-Michael Key
— Buddy the Unicorn (voice)
Michael Shannon
— Charlie the Train (voice) / Willie (voice)
Patton Oswalt
— Strappy (voice)
Clint Howard
— George (voice)
Sergey Zhuravsky
— Buddy the Unicorn
Madison Polan
— Hannah
Bryson JonSteele
— Derek
Seamus Flynn
— Timothy
Bennie Taylor
— Mailman Miles
Mark Aaron Buerkle
— Therapist (Day Player)
Phuong Kubacki
Luke Speakman
— Josh
Tristan Borders
— Oliver
Caleb Williams
— Wade
Conner Stumm
— Mailman Justin
Eric Salazar
— Dad
Lynette Eklund
— Puppeteer
Tory Jacqui Malone
— Tyler
Rachel Appelbaum
— Clocky / Mr. Mailbox
Cedwan Hook
— Betty Bunny Puppeteer
Jonathan Yurco
— Dark Buddy
Frank Brown Jr.
— Father