X Meets Y/Theatre

Examples of X Meets Y/Theatre include:

The musical Avenue Q has been described as "South Park + Sesame Street + Friends", while the creators have described it as Sesame Street meets Rent.
Adam Tettle's Misha is best described as It's a Wonderful Life + Superbad. Naturally, it's Better Than It Sounds.
A Night in the Old Markeplace is basically Fiddler on the Roof meets The Black Rider.
A Shoggoth on the Roof is Fiddler on the Roof meets H.P. Lovecraft. Literally.
The Fantasticks has been described as "Romeo and Juliet meets Reality".
Zombie Prom is Grease meets zombies. Actually, there's only one zombie.
Little Shop of Horrors is best summed up as Edgar Allen Poe meets a Disney musical. Which makes sense, considering Alan Menken and Howard Ashman did the score.
Dog Sees God is You're a Good Man Charlie Brown meets Spring Awakening.
The Skin of Our Teeth: Our Town meets Hellzapoppin.
Pippin is Candide meets The Fantasticks.
Starship is The Little Mermaid meets Aliens
The Green Goblin in Spider-Man: Turn Off the Dark has been described as looking like "the bad guy from the end of The Mask meets Megatron from Michael Bay's Transformers movie meets Nathan Lane in The Birdcage."