Twilight mentions "Claw-achella", a reference to the Coachella music festival.
Starlight Glimmer and Sunburst's use of a drawn circle to "materialize an object that was lost in the past", as well as the ritual's result in failure, mirror the similar plot point of the anime/manga series Fullmetal Alchemist in which lead characters Edward and Alphonse Elric use a Transmutation Circle in an attempt to resurrect their dead mother.
In one of the bubbles of Celestia's dreamscape, Dr. Hooves is seen in a hedge maze avoiding a statue trying to catch him. This is a reference to the Weeping Angels from the sci-fi TV series Doctor Who.
Pinkie Pie's expression "You can lead a yak to water, but you better not let him know you're doing it" is a play on the real-life expression "You can lead a horse to water, but you can't make it drink".
When Pinkie, Rainbow, and A. K. Yearling travel to Somnambula, a map with a moving red line marks their journey, identical to the traveling scenes in the Indiana Jones films—the same allusion to which was made in Daring Don't.
Just as the legends in Campfire Tales were influenced by real-life cultures, the legend of Somnambula draws influences from Ancient Egypt, such as the ponies' clothes and makeup, the pyramids, and the sphinx.
Somnambula shares her name with a G1 villain, a human witch who steals youth from others.
The sphinx's bridge challenge for Somnambula, and Dr. Caballeron's challenge for Daring Do, bears a resemblance to the "Path of God" challenge in Indiana Jones and the Last Crusade.
The title is a play on the expression "a wealth of information".
According to Fluttershy, ancient Equestrian healers like Mage Meadowbrook would wear bird masks to prevent them from getting sick themselves. Twilight and Fluttershy also wore bird masks in the episode to protect themselves from Swamp Fever. This all alludes to the real life medieval Plague doctors who would wear bird shaped masks to prevent infection from the Black Death.
The title alludes to the phrase "once upon a time", a common opening line in fairy tales.
Twilight recalls Shining Armor getting sick on a ride at Pony Island, a reference to Coney Island, a borough of Brooklyn best known for its beaches, boardwalk, and especially its amusement parks Astroland and Luna Park.
Shining Armor does the famous "I'm flying" scene from Titanic while on the airship.
The Neighagra Falls barrel-jumping activity alludes to Annie Edson Taylor, the first woman to survive going over Niagara Falls in a barrel.
The nature of the "darkness" that possesses Stygian as a parasitic "entity" that promises power to its host, refuses to let go, and creates constructs from its substance resembles the Symbiotes from Marvel Comics, most notably Venom and Carnage.