
Re: Musical numbers about Halloween icons...
If you want witches, then Wicked, The Wiz...
Some other musicals you might want to consider are Rocky Horror (classic around this time), Young Frankenstein, Addams Family, Sweeney Todd, Jekyll and Hyde, Assassins, Ghost: The Musical, Next to Normal (maybe), Bat Boy, Reefer Madness, Carrie, Dracula, Little Shop, Heathers (maybe), Spring Awakening (maybe), Zombie Prom (my guilty pleasure

)
There's also Spooky Mormon Hell Dream from Book of Mormon.
Hope this helped!