Bill and Aldo Say Mamma Mia! is a crossover that will be made by N/A. It is unknown when to appear on YouTube in the future.
Bill, Aldo, Bev, Fred the Penguin, Ed, Oly, Waddle, Stan Marsh, Kyle Broflovski, Eric Cartman, Kenny McCormick, Butters Stotch, Big Bird, Oscar the Grouch, Snuffy, Elmo, Zoe, Grover, Telly, Rosita, Baby Bear, Abby Cadabby, Bert and Ernie, Cookie Monster, Prairie Dawn, Count von Count, Bear, Ojo, Pip and Pop, Treelo, Tutter, Bugs Bunny, Daffy Duck, Porky Pig, Sylvester, Tweety, Foghorn Leghorn, Garfield, Odie, and the rest meet Sophie who is ought to get married during the summer.
- Ike Broflovski, Wendy Testaburger, The Simpsons (Homer, Marge, Bart, Lisa, and Maggie), Milhouse van Houten, Krusty the Clown, Mickey Mouse, Minnie Mouse, Goofy, Donald Duck, Daisy Duck, Pluto, Max Goof, Clarabelle Cow, Horace Horseollar, Lola Bunny, The Vultures, Jiminy Cricket, Zazu, Emperor Kuzco, Pacha, Kronk, Jean-Bob, Speed, Puffin, Peanut Otter, Butter Otter, Jelly Otter, Ernest Otter, Opal Otter, Flick Duck, Munchy Beaver, Pinch Raccoon, Scootch Raccoon, Ootsie and Bootsie, Aunt Nanner, Olie Polie, Zowie Polie, Percy Polie, Bromley Polie, Pappy Polie, Billy Bevel, The Little Einsteins (Leo, June, Annie, and Quincy), Jake the Pirate, Izzy, Cubby, Skully, Roger Rabbit, Baby Herman, Charlie Barkin, Itchy Itchiford, Yakko Warner, Wakko Warner, Dot Warner, Chloe King, Alek Petrov, Amy, Paul, Jasmine (The Nine Lives of Chloe King), and Brian Rezza will guest star in this film.
- Sitting Ducks and Mamma Mia! were made by Universal.