Expy: Most of the characters are based on the classic Oz characters, although it is revealed that D.G. is a direct descendant of Dorothy Gale. It is implied the other characters are descendants of the original as well.
D.G. = Dorothy Gale (averted due to being actually related to Dorothy). To an extent, she also is an expy of Tip (Ozma who was disguised as a boy and sent away) with her forgotten heritage, tomboy behavior, and troublemaking.
Azkadellia = The Wicked Witch of the West (although she is possessed by the actual witch).
The only characters in the party with surnames? Dorothy Gale and Nick Chopper (the Tin Woodsman). The only ones in the party with surnames in the mini? D. G. (Gale) and Wyatt Cain (the Tin Man)
D.G. and her parents live in Kansas, on the same farm where Dorothy lived.
The police officer who gives D.G. is a speeding ticket is named Officer Gulch, after Miss Gulch from The Wizard of Oz.
D.G. works in a diner like Ashanti in The Muppets' Wizard of Oz. Her work outfit resembles Dorothy's dress from the 1939 film, though the white and blue gingham dress was also referenced in the book.
D.G. refers to Hank as "Popsicle". Glinda called her father this nickname in Wicked.
Emily shows D.G. has numerous travel brochures, one of which is to Australia, where Uncle Henry and Dorothy's relatives lived in Ozma of Oz, which started with Dorthy and Uncle Henry taking a trip there.
Azkadellia's fortress is based on the Wicked Witch's castle from the 1939 film.
The Emerald of the Eclipse resembles a miniaturised version Emerald City from the 1939 film.
The tank which Azkadellia uses to show the visions of the Viewers is a nod to the Wicked Witch's crystal ball and all-seeing eye.
The arrival of the storm in Kansas involves several symbolical nods to the Scarecrow (a scarecrow's head falls off), the Tin Woodman (a rusted heart-shaped number plate), and the Cowardly Lion (a cat runs away in fear).
Dorothy's house is Number 39 - a nod to the year 1939, when The Wizard of Oz was released.
The Munchkins seen are part of the "Eastern Resistance Guild" - a possible nod to the Lollipop Guild from the film.
Munchkin Country was also in the eastern part of Oz, and the original Munchkins intitially mistook Dorothy for a powerful (and potentially dangerous) Munchkin sorceress due to her blue and white clothing (blue being Munchkin colors, white only worn by sorcerers/sorceresses), and called the North Witch to detain and question her.
Glitch is introduced with a missing brain and being tied up like the Scarecrow.
Like Nick Chopper before him, he is the party's strongest fighter. He also is very unlucky in love. Cain is too late to save his wife. Nick just found out his girlfriend two-timed him and then ran off with someone else.
The term "Tin Man" is used for the O.Z.'s former police officers.
Lavender Eyes is trapped in a bubble of sorts by Azkadellia - a nod to her mode of transport from the 1939 film.
Milltown's robotic residents may be a nod to Tik Tok, one of the first robots in modern literature.
Their half-human, half robot appearance could also be a reference to Klu-Klip's experiments in The Tin Woodsman of Oz where he made a Frankenstein-esque creature out of Nick and Capt. Fyter's hacked off body parts and robotic pieces.
The Mobats (or Monkey Bats) are the Flying Monkeys.
The Mystic Man appears at first as a giant holographic head and then appears from a ball of fire.
Glitch points out an off-screen rainbow - a nod to "Somewhere Over the Rainbow".