In one of the very first shots of the film, there’s a rainbow over Oz. This is perhaps the most obvious Easter egg and a direct callback to The Wizard of Oz and “Somewhere Over the Rainbow”—it immediately lets audiences know the stories are intertwined.

All the main characters from The Wizard of Oz make a cameo in Wicked, as the camera pans over Oz right before “No One Mourns the Wicked.” This is a clear indication of what’s coming in Part 2, which is Elphaba and Glinda’s POV of the events of The Wizard of Oz.

The "Wicked" movie references the musical and "The Wizard of Oz." You probably caught its biggest cameos, but you may have missed other easter eggs.