When Barry Allen and Oliver Queen wake up one morning and realize they have swapped bodies with each other, the two set off to find out what disturbed the timeline to cause such a shift. However, things quickly go from bad to worse when they present their case to Team Flash and the gang doesn’t believe them. Barry and Oliver realize they need Supergirl’s help and travel to Smallville on Earth-38 where they end up meeting Kara’s cousin, Clark Kent, and intrepid reporter, Lois Lane.
After Barry and Oliver switch places, Barry refers to it by saying "Man, what a total "Freaky Friday." No, wait, we didn't switch bodies. It's more of a "Quantum Leap"". In the Freaky Friday movies the characters minds swap bodies. In the Quantum Leap TV series, Sr Sam Beckett changes places with people when he's still in his own body but people perceive him to be the other person, which is closer to their situation.
A major Smallville easter egg appears in this episode where the show's theme song "Save Me" by Remy Zero was played during the introduction of the Earth-38 Smallville, with a farm location used in Smallville also reused. In addition, the Smallville version of Green Arrow's suit appeared in the cold open on the corpse of the Earth-90 Green Arrow.
Lois calls Clark "Smallville", referencing Clark's nickname given to his comic book counterpart by Lois Lane.
When Barry tried to talk like Oliver, he said "wear a mask", which is what Oliver said to him in "Pilot"
The scene when Barry shot Oliver with Arrows is almost an exact replica of the original scene from "Flash vs. Arrow", with Barry and Oliver switching dialogues and roles.
The shot that shows the remote control bows is recycled from that episode, with only a few changes through edits.
It's also the first in-universe appearance of Batwoman, from Earth-1's Gotham City, showing up in the final scene.
When Oliver was about to faint, Iris said "Nanites, courtesy of Ray Palmer", which is the same thing Oliver said to Reverse-Flash in "Rogue Air".
At one point Ralph says, "something weird's going on, and it ain't even Tuesday". This fourth-wall-breaker is a nod to the fact that The Flash typically air on Tuesday nights, but that the show swapped time slots with Supergirl for the crossover event.
Referencing to A.M.A.Z.O., Ralph says "So an evil copycat Gort is coming to klaatu barada kick-to our asses.". This line is a reference to the 1951 film The Day the Earth Stood Still and its character Gort, by also using the phrase "klaatu barada" from it.
During the same conversation, Cisco refers to the situation by saying "How do you stop a T-3000 that kills for breakfast?", which is a reference to the Terminator franchise.
When the Flash was distracting A.M.A.Z.O. the chase leads to a scaffolding area, which bears resemblance to where the Prism was located during Crisis on Earth-X, Part 2.
A Superman The Movie Easter egg is shown where Cisco asks Clark who he is, Clark replies, "A friend".