Parody Assistance

A great honor for anyone working on a Parody is when the creator or anyone else involved with the original goes beyond granting the parodist permission (and even enjoying said work) and instead actually helping them out with their parody. This can be as simple as lending sets or as drastic as directly working with the parodist, such as singing in a duet.

Related to Adam Westing.

Film

 * George Lucas has done this a few times, from allowing original music from Star Wars to be used in parodies (such as Spaced) to actually appearing in parodies, as in Robot Chicken.
 * In The Brady Bunch Movie, several of the original Brady kids (and Alice) made cameos (There were also reportedly two deleted scenes, one featuring Mike Lookinland "Bobby", and Susan Olsen "Cindy").
 * When Mel Brooks made Young Frankenstein, he was able to film in the original studios, on the original sets, and using the original props of the classic movies he was spoofing.
 * In Beverly Hills Cop 3, the Wonder World theme park's song, which spoofs the Disney Land song "It's a Small World After All", was written by "It's a Small World"'s original composers Richard and Robert Sherman.

Live Action TV

 * When The Drew Carey Show was going to do an episode making fun of sci-fi conventions and the fans who go to them in costume, they wanted to have a couple of characters dress up as aliens from Babylon Five. The creators of B5 agreed... and sent their own makeup people to do the alien makeup effects.
 * Chris Ballew, lead singer of the group The Presidents of the United States, showed up on Bill Nye the Science Guy to sing "Farm Food", which spoofed the POTUS song "Peaches".
 * Anneka Rice of Challenge Anneka made a cameo appearance in the KYTV spoof Challenge Anna.

Music

 * Happens with Weird Al Yankovic a lot. For example, his music video for "Fat", a parody of Michael Jackson's "Bad", uses the subway set for a parody from Moonwalker called "Badder", which Jackson granted Al permission to borrow. Also, "I Lost on Jeopardy" ("Jeopardy" by the Greg Kihn Band) has Art Fleming and Don Pardo (the host and announcer from the original 1960s version) reprise their respective roles in the video for it, and even Greg Kihn himself appears in the end.
 * Madonna wrote the first verse of his "Like a Surgeon" and sent it to him so he would do it.
 * Madonna didn't just help Al parody her own stuff; she also appears in his video making fun of Lady Gaga's "Born this Way", which of course is clearly inspired by Madonna's "Express Yourself".
 * Mark Knopfler of Dire Straits agreed to allow Al to parody "Money for Nothing" on condition that Knopfler himself play his guitar parts from the original song in the parody.
 * He has similar success with his unfocused pastiches, in which the song evokes the artist's style without having the same tune. Examples include Ben Folds playing piano on "Why Does This Always Happen To Me?", Dweezil Zappa playing guitar for the Frank Zappa-esque "Genius In France", The Doors keyboardist Ray Manzarek contributing to "Craigslist", and Taylor Hanson playing piano on "If That Isn't Love".
 * George Harrison appeared in The Rutles.
 * Country artist Cledus T. Judd, who does mostly parodies, has had country stars appear in his videos, such as Toby Keith in the parody of "How Do You Like Me Now?!", "How Do You Milk A Cow".
 * Even some of Judd's parodies feature the original artist in the recording, such as Brad Paisley on "More Beaver" (parody of "Me Neither"), George Jones on "I Was Country When Country Wasn't Pop" (parody of George Jones and Barbara Mandrell's "I Was Country When Country Wasn't Cool"), Toby Keith on "I Love NASCAR" (parody of "I Love This Bar") and Ronnie Dunn on "Garth Must Be Busy" (Brooks and Dunn's "God Must Be Busy").
 * Hello Dolly star Carol Channing appeared on Forbidden Broadway Vol. 3 in a magnificent invocation of this trope.

Newspaper Comics

 * Jim Davis has contributed a few strips to Garfield Minus Garfield.

Western Animation

 * Saturday Night Live's School House Rock parody "Conspiracy Theory Rock" had Jack Sheldon reprise his role as the main singer.
 * The Simpsons episode "The Day the Violence Died" contained a parody of "I'm Just a Bill" with Sheldon singing it, as well.
 * In "E-I-E-I-(Annoyed Grunt)", the B-52s parody their own "Love Shack" as "Glove Slap", while later episodes featured Jackson Browne and the Baha Men parodying their own respective work.
 * Sheldon lent his voice to Family Guy's parodies of SHR, as well.
 * The Bob's Burgers episode "The Belchies" features a song in the end credits that's a send-up of "The Goonies 'R' Good Enough" sung by Cyndi Lauper.
 * The Futurama episode "Deep South" is set in Atlanta, Georgia, which is now a submerged city filled with mer-people. Helping to explain this is Donovan, parodying his own song "Atlantis" as "Atlanta."