Suggestions by @kazpalys

Keegan-Michael Key

as Slime in IF 2

Richard Jenkins

as Art Teacher in IF 2

Bill Hader

as Banana in IF 2

Matt Damon

as Flower in IF 2

Bradley Cooper

as Ice in IF 2

George Clooney

as Spaceman in IF 2

Emily Blunt

as Unicorn in IF 2

Awkwafina

as Bubble in IF 2

Louis Gossett Jr.

as Lewis in IF 2

Phoebe Waller-Bridge

as Blossom in IF 2

Steve Carell

as Blue in IF 2

Catharine Daddario

as Bea's mother in IF 2

Bobby Moynihan

as Jeremy in IF 2

Liza Colón-Zayas

as Janet in IF 2

Alan Kim

as Benjamin in IF 2

Fiona Shaw

as Bea's grandmother in IF 2

John Krasinski

as Bea's unnamed father in IF 2

Ryan Reynolds

as Cal in IF 2

Cailey Fleming

as Bea in IF 2

Dillon Francis

as DJ Airy in IF 2