Elseworlds, Part 1

The episode is the first of the three-part crossover with the ninth episode of the seventh season of, and the ninth episode of the fourth season of being the rest of this year's crossover

Synopsis
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.

Trivia

 * This is the first episode of the series to not feature after being promoted to series regular.
 * The episode was previously titled "Elseworlds: Hour One".
 * 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, Dr. 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.
 * Noticeably, despite Barry obtaining Oliver's more muscular build from inheriting his life, Oliver did not obtain Barry's slim frame, but rather remained the same.
 * 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 Thirty-Eight Smallville, with the farm location used in Smallville also reused. In addition, the Smallville version of Green Arrow's suit appeared in the opening scene on one of the corpses.
 * 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.
 * The scene when Barry shot Oliver with arrows is almost an exact replica of the original scene from, 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.
 * When Oliver is about to faint, Iris says "Nanites, courtesy of Ray Palmer", which is the same thing Oliver said to the Reverse-Flash in.
 * When Team Flash realizes something weird's going on, Ralph says, "Man, it's not even Tuesday". This fourth-wall-breaker is a nod to the fact that episodes of typically air on Tuesday nights, but that the show swapped time slots with, instead airing on Sunday night, for the Elseworlds crossover event.
 * Referencing 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, 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.
 * When Cisco asks who Clark is, Clark replies "A friend", referencing the 1978 film Superman.
 * A part of the Super Friends intro plays when Clark does the infamous Superman "S" reveal.
 * The opening scene from this episode previously appeared at the conclusion of the episode,  episode , and  episode.