For instance, imagine a version of “Little Shop of Horrors” with:
~Poison Ivy as Seymour
~Harley Quinn as Audrey
~Joker as Orin
~Floronic Man as Mr. Mushnik
Or “The Sound of Music” with:
~Catwoman as Maria
~Batman as Baron von Trapp
~The Robins and Batgirls as the Von Trapp Children
~Wonder Woman as the Mother Superior
~Helena Bertinelli as Rolf the messenger boy
Or “Oklahoma!” with the cast of Smallville, “Chicago” set in Arkham Asylum… the possibilities are endless!
Sweeney Todd: The Demon Barber of Fleet Street
Sweeney Todd - The Joker
Mrs. Lovett - Harley Quinn
Judge Turpin - Batman
Beadle Bamford - Dick Grayson (cos he is the best Robin)
Signor Adolfo Pirelli/Daniel O’Higgins - Edward Nygma
Oh this is a brilliant thread, and the musical theater in me is screaming at my PC - Good job, @VengeanceNightBatman!! 
I don’t know the whole of it and am not into musicals in a big way, but Batman would find his way into the H.M.S. Pinafore somehow. “If his brow should furrow and his lip should curl!” applies to Batman I feel.
Les Miserables with Cat Woman as Fantine and Jor El as Javert…
For Phantom Of The Opera…
Two-Face as The Phantom
Donna Troy as Christine Dáee
Dick Grayson as Rauol
Supergirl as Meg
Catwoman as Carlotta
Bruce Wayne & Alfred Pennyworth as the two managers
Les Misérables
Hal Jordan as Jean Valjean
Sinestro as Javert
Barbara Gordon as Fantine
The Penguin & Harley Quinn as the couple who sings Master of the house
Barry Allen as Marius
Zatanna as Eponie
@Harleys Puddin - What, no “JASON Todd, Demon Barber of Fleet Street?” Kudos on the casting choices, though.
@TheDemonEtrigan - Har, har.
@Reaganfan 78 - Good work! Especially love the Phantom one.
Thankyou, that was fun! 
Dr Horrible
--
Mr Mxyzptlk as Dr Horrible
Kara as Penny
Mon-El as Captain Hammer
Comet as Bad Horse
Lobo, Jonah Jex and the Killer of Saints as Bad Horse's messengers
Aquaman as Moist
Stargirl, Starfire and Beast Boy as GroupiesHamilton
Superman as George Washington
Superboy (Connor) as Hamilton
Miss Martian as Eliza
Robin Damian as Jefferson
Alexander Luthor as Burr
Let’s go with an obvious choice: Stephen Sondheim’s Assassins:
The Balladeer: Ra’s al Ghul
John Wilkes Booth: Deathstroke
Sara Jane Moore: Harley Quinn
Guisseppe Zangara: KGBeast
Charles Guiteau: Deadshot
Squeaky Fromme: Cheshire
Lee Harvey Oswald: Malcolm Merlyn (as played by John Barrowman, naturally)
‘All you have to do is pull your little finger…’
Rocky horror
Supes and Lois as Brad and Janet
Batman as Dr Frank N. Furter
Bizzaro as Eddie
Reverse Flash for Riff Raff ( he can do a time warp better than anyone)
Jim Gordon Dr. Scott
Jimmy Olson as Rocky Horror
Zantanna as Magenta
Wouldn’t J’onn J’onnz make more sense as Dr. Furter?
Nothing completes a fishnet ensemble like the cowl
Omg @HarleysPuddin beat me too it, that was my idea lol!
