In It’s Not Easy Being Green, according to the poster, Walsh's circus is called The Omaha Circus and Freak Show. In The Wonderful Wizard of Oz novel, Omaha was the name of the Wizard's birthplace. The circus and freak show acts listed are:
"The sorcerer's black tent"
The Feejee mermaid, an object comprising the torso and head of a juvenile monkey sewn to the back half of a fish. During the 1800s, it was a common feature of sideshows, where it was presented as a version of a mermaid.
The Bottle Imp ("living human head confined in a glass bottle"): The Bottle Imp is an 1891 short story by Robert Louis Stevenson. In it, the protagonist buys a bottle with an imp inside that grants wishes. However, the bottle is cursed; if the holder dies bearing it, their soul is forfeit to hell.
The Dog Faced Boy, a reference to Jo-Jo the Dog-Faced Boy, a famous Russian sideshow performer during the 1800s, who suffered from the medical condition hypertrichosis.
The bearded lady: Women with visible beards have a rich history in the sideshows of the 19th and early 20th centuries.
The flying monkeys.