Guest appearances in other Hanna-Barbera and Warner Bros. productions

The following is a list of official guest appearances (whether canon or not) in other productions produced by Hanna-Barbera and later Warner Bros. Animation

Films

Looney Tunes: Back in Action

Shaggy Rogers and Scooby-Doo (voiced by Casey Kasem & Frank Welker, respectively) make cameo appearances, complaining to Matthew Lillard about how he portrayed Shaggy in Scooby-Doo: The Movie. Shaggy told Lillard he made him sound like a space cadet and warned if he goofed on him in the sequel, he would come after him and Scooby said he'd give him a Scooby Snack before proceeding to growl at Lillard viciously.

The LEGO Movie 2: The Second Part

A LEGO version of Velma had a brief cameo, in which she only had a single line. She was voiced by Trisha Gum.

Television

Duck Dodgers

During a montage in Surf the Stars, featuring Brian Wilson's song "Believe in Yourself", Mystery Inc., followed by Scooby-Doo, Where Are You! monsters (including Ghost of Captain Cutler, Ghost of Redbeard, the witch, Creeper, and the Green Ghost), all run past the screen.

Dynomutt, Dog Wonder

The series premiered alongside The Scooby-Doo Show in 1976. To capitalize on this, Mystery Inc. gang guest starred in Everyone Hyde!, What Now, Lowbrow?, and The Wizard of Ooze. The main cast reprised their roles, which were Don Messick, Kasem, Welker, Heather North, and Pat Stevens.

The Grim Adventures of Billy & Mandy

Scooby-Doo appeared twice in The Grim Adventures of Billy and Mandy, in the episodes Reap Walking and Keeper of the Reaper, the former was a non-speaking cameo with the rest of the gang, while the latter he was voiced by Welker.

Johnny Bravo

The gang were guest stars in Bravo Dooby-Doo. Welker, Kasem, and North reprised their roles as Fred, Shaggy, and Daphne, respectively. While new actors B.J. Ward and Hadley Kay were hired for Velma and Scooby, respectively. Kay then reprised the role for a Scooby cameo in 'Twas the Night.

Harvey Birdman, Attorney at Law

The gang were guest stars in Shaggy Busted. The cast included Scott Innes as Scooby and Shaggy, Frank Welker as Fred, Grey DeLisle as Daphne, Ward as Velma, with a cameo from Scrappy-Doo, also voiced by Innes.

Batman: The Brave and the Bold

The gang are guests in a segment of Bat-Mite Presents: Batman's Strangest Cases!, in a parody of The New Scooby-Doo Movies. The cast included Welker as Scooby and Fred, Lillard as Shaggy, DeLisle as Daphne, and Mindy Cohn as Velma.

Sabrina the Teenage Witch (live-action)

In Sabrina Unplugged, when Sabrina is caught by the office webcam using her powers, she magically enters Leonard's computer to destroy the evidence and meets up with Shaggy and Scooby (voiced by Innes and Welker, respectively). He asks her if she can get them off as a screensaver, as they're embarrassed. Both shows aired on The WB at the time.

Supernatural

The gang are guests in Scoobynatural, when three of the main characters of Supernatural are sucked into the episode A Night of Fright is No Delight. The cast included Welker as Scooby and Fred, Lillard as Shaggy, Griffin (formerly DeLisle), and Kate Micucci as Velma.

OK K.O.! Let's Be Heroes

In the episode Monster Party, the main students of Miss Grimwood's Finishing School for Ghouls in the TV film Scooby-Doo and the Ghoul School guest star. The cast for the girls include Pat Musick, Russi Taylor, Susan Blu, Kristen Li, Natalie Palamides as Elsa Frankenteen, Phantasma, Sibella, Tanis, and Winnie Werewolf, respectively.

Teen Titans Go!

The gang are guest stars in the episode Cartoon Feud. The cast is Welker as Scooby and Fred, Lillard as Shaggy, Griffin as Daphne, and Micucci as Velma.