Suggestions by @chrisdeaver

Thor

as Guest Stars in Gravity Falls Return

Captain America (Marvel Cinematic Universe)

as Guest Stars in Gravity Falls Return

Iron Man (Marvel Cinematic Universe)

as Guest Stars in Gravity Falls Return

Justin Roiland

as Morty Smith in Gravity Falls Return

Justin Roiland

as Rick Sanchez in Gravity Falls Return

Alex Hirsch

as Bill Cipher in Gravity Falls Return

Linda Cardellini

as Wendy Courdory in Gravity Falls Return

Alex Hirsch

as Soos Ramirez in Gravity Falls Return

J.K. Simmons

as Ford Pines in Gravity Falls Return

Alex Hirsch

as Grunkle Stan in Gravity Falls Return

Kristen Schaal

as Mabel Pines in Gravity Falls Return

Jason Ritter

as Dipper Pines in Gravity Falls Return

Jack Black

as Slappy in Chucky Vs Leperchaun Vs Slappy

Warwick Davis

as Leprechaun in Chucky Vs Leperchaun Vs Slappy

Brad Dourif

as Chucky in Chucky Vs Leperchaun Vs Slappy

Debi Derryberry

as Jimmy Neutron in Space Jam But With Nickelodeon Characters

Tom Kenny

as Spongebob Squarepants in Space Jam But With Nickelodeon Characters

LeBron James

as Himself in Space Jam But With Nickelodeon Characters

Jason Maybaum

as Lincoln Loud in Nicktoons (R-Rated Animated Film)

Mr. Lawrence

as Plankton in Nicktoons (R-Rated Animated Film)